diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/AccountBuilderTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/AccountBuilderTest.java
index 7a59346b..9b5361c3 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/AccountBuilderTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/AccountBuilderTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 import static org.shredzone.acme4j.toolbox.TestUtils.getJSON;
 import static org.shredzone.acme4j.toolbox.TestUtils.url;
 import static uk.co.datumedge.hamcrest.json.SameJSONAs.sameJSONAs;
@@ -41,8 +41,8 @@ import org.shredzone.acme4j.toolbox.TestUtils;
  */
 public class AccountBuilderTest {
 
-    private URL resourceUrl = url("http://example.com/acme/resource");
-    private URL locationUrl = url("http://example.com/acme/account");
+    private final URL resourceUrl = url("http://example.com/acme/resource");
+    private final URL locationUrl = url("http://example.com/acme/account");
 
     /**
      * Test if a new account can be created.
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/AccountTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/AccountTest.java
index 56fd1f21..b23edecd 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/AccountTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/AccountTest.java
@@ -13,8 +13,10 @@
  */
 package org.shredzone.acme4j;
 
+import static java.util.Collections.emptyList;
+import static java.util.Collections.singletonList;
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 import static org.shredzone.acme4j.toolbox.TestUtils.getJSON;
 import static org.shredzone.acme4j.toolbox.TestUtils.url;
@@ -25,9 +27,7 @@ import java.net.HttpURLConnection;
 import java.net.URI;
 import java.net.URL;
 import java.security.KeyPair;
-import java.util.Arrays;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.Iterator;
 import java.util.concurrent.atomic.AtomicBoolean;
 
@@ -51,9 +51,9 @@ import org.shredzone.acme4j.toolbox.TestUtils;
  */
 public class AccountTest {
 
-    private URL resourceUrl  = url("http://example.com/acme/resource");
-    private URL locationUrl  = url(TestUtils.ACCOUNT_URL);
-    private URL agreementUrl = url("http://example.com/agreement.pdf");
+    private final URL resourceUrl  = url("http://example.com/acme/resource");
+    private final URL locationUrl  = url(TestUtils.ACCOUNT_URL);
+    private final URL agreementUrl = url("http://example.com/agreement.pdf");
 
     /**
      * Test that a account can be updated.
@@ -76,7 +76,7 @@ public class AccountTest {
             public int sendSignedPostAsGetRequest(URL url, Login login) {
                 if (url("https://example.com/acme/acct/1/orders").equals(url)) {
                     jsonResponse = new JSONBuilder()
-                                .array("orders", Arrays.asList("https://example.com/acme/order/1"))
+                                .array("orders", singletonList("https://example.com/acme/order/1"))
                                 .toJSON();
                 } else {
                     jsonResponse = getJSON("updateAccountResponse");
@@ -96,7 +96,7 @@ public class AccountTest {
 
             @Override
             public Collection<URL> getLinks(String relation) {
-                return Collections.emptyList();
+                return emptyList();
             }
 
             @Override
@@ -154,8 +154,8 @@ public class AccountTest {
             @Override
             public Collection<URL> getLinks(String relation) {
                 switch(relation) {
-                    case "termsOfService": return Arrays.asList(agreementUrl);
-                    default: return null;
+                    case "termsOfService": return singletonList(agreementUrl);
+                    default: return emptyList();
                 }
             }
 
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/AcmeJsonResourceTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/AcmeJsonResourceTest.java
index 8307682d..4278a07d 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/AcmeJsonResourceTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/AcmeJsonResourceTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
-import static org.junit.Assert.assertThat;
 import static org.shredzone.acme4j.toolbox.TestUtils.getJSON;
 import static org.shredzone.acme4j.toolbox.TestUtils.url;
 
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/AcmeResourceTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/AcmeResourceTest.java
index cd64dfac..65d2d8da 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/AcmeResourceTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/AcmeResourceTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 
 import java.io.ByteArrayInputStream;
@@ -22,6 +22,7 @@ import java.io.ByteArrayOutputStream;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
 import java.net.URL;
+import java.nio.charset.StandardCharsets;
 
 import org.junit.Test;
 import org.shredzone.acme4j.toolbox.TestUtils;
@@ -73,7 +74,7 @@ public class AcmeResourceTest {
         }
 
         // Make sure there is no PrivateKey in the stream
-        String str = new String(serialized, "iso-8859-1");
+        String str = new String(serialized, StandardCharsets.ISO_8859_1);
         if (str.contains("Ljava/security/PrivateKey")) {
             fail("serialized stream contains a PrivateKey");
         }
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/AuthorizationTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/AuthorizationTest.java
index f609090c..a7f928a9 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/AuthorizationTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/AuthorizationTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 import static org.shredzone.acme4j.toolbox.AcmeUtils.parseTimestamp;
 import static org.shredzone.acme4j.toolbox.TestUtils.getJSON;
@@ -47,7 +47,7 @@ public class AuthorizationTest {
     private static final String SNAILMAIL_TYPE = "snail-01"; // a non-existent challenge
     private static final String DUPLICATE_TYPE = "duplicate-01"; // a duplicate challenge
 
-    private URL locationUrl = url("http://example.com/acme/account");
+    private final URL locationUrl = url("http://example.com/acme/account");
 
     /**
      * Test that {@link Authorization#findChallenge(String)} finds challenges.
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/CertificateTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/CertificateTest.java
index 2c4c04d7..92b58b17 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/CertificateTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/CertificateTest.java
@@ -13,9 +13,9 @@
  */
 package org.shredzone.acme4j;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.notNullValue;
-import static org.junit.Assert.assertThat;
 import static org.shredzone.acme4j.toolbox.TestUtils.getJSON;
 import static org.shredzone.acme4j.toolbox.TestUtils.url;
 import static uk.co.datumedge.hamcrest.json.SameJSONAs.sameJSONAs;
@@ -45,8 +45,8 @@ import org.shredzone.acme4j.toolbox.TestUtils;
  */
 public class CertificateTest {
 
-    private URL resourceUrl = url("http://example.com/acme/resource");
-    private URL locationUrl = url("http://example.com/acme/certificate");
+    private final URL resourceUrl = url("http://example.com/acme/resource");
+    private final URL locationUrl = url("http://example.com/acme/certificate");
 
     /**
      * Test that a certificate can be downloaded.
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/IdentifierTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/IdentifierTest.java
index 214b2c87..42251460 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/IdentifierTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/IdentifierTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
-import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 
 import java.net.InetAddress;
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/LoginTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/LoginTest.java
index b0d3a3ae..42051f5d 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/LoginTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/LoginTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 import static org.mockito.Mockito.*;
 import static org.shredzone.acme4j.toolbox.TestUtils.getJSON;
 import static org.shredzone.acme4j.toolbox.TestUtils.url;
@@ -39,7 +39,7 @@ import org.shredzone.acme4j.toolbox.TestUtils;
  */
 public class LoginTest {
 
-    private static final URL resourceUrl = url("https://example.com/acme/resource/123");
+    private final URL resourceUrl = url("https://example.com/acme/resource/123");
 
     /**
      * Test the constructor.
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/OrderBuilderTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/OrderBuilderTest.java
index eaf2c1b7..caba6664 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/OrderBuilderTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/OrderBuilderTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 import static org.shredzone.acme4j.toolbox.AcmeUtils.parseTimestamp;
 import static org.shredzone.acme4j.toolbox.TestUtils.getJSON;
@@ -41,8 +41,8 @@ import org.shredzone.acme4j.toolbox.TestUtils;
  */
 public class OrderBuilderTest {
 
-    private URL resourceUrl  = url("http://example.com/acme/resource");
-    private URL locationUrl  = url(TestUtils.ACCOUNT_URL);
+    private final URL resourceUrl  = url("http://example.com/acme/resource");
+    private final URL locationUrl  = url(TestUtils.ACCOUNT_URL);
 
     /**
      * Test that a new {@link Order} can be created.
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/OrderTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/OrderTest.java
index 34e912d0..578cac11 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/OrderTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/OrderTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 import static org.shredzone.acme4j.toolbox.AcmeUtils.parseTimestamp;
 import static org.shredzone.acme4j.toolbox.TestUtils.getJSON;
 import static org.shredzone.acme4j.toolbox.TestUtils.url;
@@ -38,8 +38,8 @@ import org.shredzone.acme4j.toolbox.TestUtils;
  */
 public class OrderTest {
 
-    private URL locationUrl = url("http://example.com/acme/order/1234");
-    private URL finalizeUrl = url("https://example.com/acme/acct/1/order/1/finalize");
+    private final URL locationUrl = url("http://example.com/acme/order/1234");
+    private final URL finalizeUrl = url("https://example.com/acme/acct/1/order/1/finalize");
 
     /**
      * Test that order is properly updated.
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/ProblemTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/ProblemTest.java
index 7adc3585..c82e0cc6 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/ProblemTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/ProblemTest.java
@@ -14,8 +14,8 @@
 package org.shredzone.acme4j;
 
 import static org.hamcrest.CoreMatchers.nullValue;
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 import static org.shredzone.acme4j.toolbox.TestUtils.url;
 import static uk.co.datumedge.hamcrest.json.SameJSONAs.sameJSONAs;
 
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/SessionTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/SessionTest.java
index 8b6d9435..870a7dda 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/SessionTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/SessionTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 import static org.mockito.Mockito.*;
 import static org.shredzone.acme4j.toolbox.TestUtils.*;
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/StatusTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/StatusTest.java
index 20b4acb4..1c79e509 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/StatusTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/StatusTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
-import static org.junit.Assert.assertThat;
 
 import org.junit.Test;
 
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/challenge/ChallengeTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/challenge/ChallengeTest.java
index f46bece8..eb5d9063 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/challenge/ChallengeTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/challenge/ChallengeTest.java
@@ -13,9 +13,9 @@
  */
 package org.shredzone.acme4j.challenge;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.notNullValue;
-import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 import static org.shredzone.acme4j.toolbox.AcmeUtils.parseTimestamp;
 import static org.shredzone.acme4j.toolbox.TestUtils.getJSON;
@@ -44,7 +44,7 @@ import org.shredzone.acme4j.toolbox.TestUtils;
  * Unit tests for {@link Challenge}.
  */
 public class ChallengeTest {
-    private URL locationUrl = url("https://example.com/acme/some-location");
+    private final URL locationUrl = url("https://example.com/acme/some-location");
 
     /**
      * Test that after unmarshaling, the challenge properties are set correctly.
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/challenge/DnsChallengeTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/challenge/DnsChallengeTest.java
index 40a09911..2cf8a201 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/challenge/DnsChallengeTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/challenge/DnsChallengeTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j.challenge;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
-import static org.junit.Assert.assertThat;
 import static org.shredzone.acme4j.toolbox.TestUtils.getJSON;
 import static uk.co.datumedge.hamcrest.json.SameJSONAs.sameJSONAs;
 
@@ -29,7 +29,7 @@ import org.shredzone.acme4j.toolbox.TestUtils;
  */
 public class DnsChallengeTest {
 
-    private Login login = TestUtils.login();
+    private final Login login = TestUtils.login();
 
     /**
      * Test that {@link Dns01Challenge} generates a correct authorization key.
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/challenge/HttpChallengeTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/challenge/HttpChallengeTest.java
index 3f68a66d..633e3a56 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/challenge/HttpChallengeTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/challenge/HttpChallengeTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j.challenge;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
-import static org.junit.Assert.assertThat;
 import static org.shredzone.acme4j.toolbox.TestUtils.getJSON;
 import static uk.co.datumedge.hamcrest.json.SameJSONAs.sameJSONAs;
 
@@ -34,7 +34,7 @@ public class HttpChallengeTest {
     private static final String KEY_AUTHORIZATION =
             "rSoI9JpyvFi-ltdnBW0W1DjKstzG7cHixjzcOjwzAEQ.HnWjTDnyqlCrm6tZ-6wX-TrEXgRdeNu9G71gqxSO6o0";
 
-    private Login login = TestUtils.login();
+    private final Login login = TestUtils.login();
 
     /**
      * Test that {@link Http01Challenge} generates a correct authorization key.
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/challenge/TlsAlpn01ChallengeTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/challenge/TlsAlpn01ChallengeTest.java
index 0ea03bed..f08fe6ea 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/challenge/TlsAlpn01ChallengeTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/challenge/TlsAlpn01ChallengeTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j.challenge;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
-import static org.junit.Assert.assertThat;
 import static org.shredzone.acme4j.toolbox.TestUtils.getJSON;
 import static uk.co.datumedge.hamcrest.json.SameJSONAs.sameJSONAs;
 
@@ -34,7 +34,7 @@ public class TlsAlpn01ChallengeTest {
     private static final String KEY_AUTHORIZATION =
             "rSoI9JpyvFi-ltdnBW0W1DjKstzG7cHixjzcOjwzAEQ.HnWjTDnyqlCrm6tZ-6wX-TrEXgRdeNu9G71gqxSO6o0";
 
-    private Login login = TestUtils.login();
+    private final Login login = TestUtils.login();
 
     /**
      * Test that {@link TlsAlpn01Challenge} generates a correct authorization key.
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/connector/DefaultConnectionTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/connector/DefaultConnectionTest.java
index 0ee99c31..a78d1440 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/connector/DefaultConnectionTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/connector/DefaultConnectionTest.java
@@ -15,8 +15,9 @@ package org.shredzone.acme4j.connector;
 
 import static java.nio.charset.StandardCharsets.UTF_8;
 import static java.time.format.DateTimeFormatter.RFC_1123_DATE_TIME;
+import static java.util.Collections.singletonList;
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 import static org.mockito.Mockito.any;
 import static org.mockito.Mockito.*;
@@ -75,9 +76,8 @@ public class DefaultConnectionTest {
     private static final Base64.Encoder URL_ENCODER = Base64.getUrlEncoder().withoutPadding();
     private static final Base64.Decoder URL_DECODER = Base64.getUrlDecoder();
 
-    private URL requestUrl = TestUtils.url("http://example.com/acme/");
-    private URL accountUrl = TestUtils.url(TestUtils.ACCOUNT_URL);
-    private NetworkSettings settings = new NetworkSettings();
+    private final URL requestUrl = TestUtils.url("http://example.com/acme/");
+    private final URL accountUrl = TestUtils.url(TestUtils.ACCOUNT_URL);
     private HttpURLConnection mockUrlConnection;
     private HttpConnector mockHttpConnection;
     private Session session;
@@ -247,8 +247,8 @@ public class DefaultConnectionTest {
     @Test
     public void testGetLink() throws Exception {
         Map<String, List<String>> headers = new HashMap<>();
-        headers.put("Content-Type", Arrays.asList("application/json"));
-        headers.put("Location", Arrays.asList("https://example.com/acme/acct/asdf"));
+        headers.put("Content-Type", singletonList("application/json"));
+        headers.put("Location", singletonList("https://example.com/acme/acct/asdf"));
         headers.put("Link", Arrays.asList(
                         "<https://example.com/acme/new-authz>;rel=\"next\"",
                         "</recover-acct>;rel=recover",
@@ -441,7 +441,7 @@ public class DefaultConnectionTest {
         when(mockUrlConnection.getContentLength()).thenReturn(jsonData.length());
         when(mockUrlConnection.getResponseCode()).thenReturn(HttpURLConnection.HTTP_FORBIDDEN);
         when(mockUrlConnection.getOutputStream()).thenReturn(new ByteArrayOutputStream());
-        when(mockUrlConnection.getErrorStream()).thenReturn(new ByteArrayInputStream(jsonData.getBytes("utf-8")));
+        when(mockUrlConnection.getErrorStream()).thenReturn(new ByteArrayInputStream(jsonData.getBytes(UTF_8)));
         when(mockUrlConnection.getURL()).thenReturn(url("https://example.com/acme/1"));
 
         session.setNonce(TestUtils.DUMMY_NONCE);
@@ -471,14 +471,14 @@ public class DefaultConnectionTest {
         String jsonData = "{\"type\":\"urn:ietf:params:acme:error:userActionRequired\",\"detail\":\"Accept the TOS\"}";
 
         Map<String, List<String>> linkHeader = new HashMap<>();
-        linkHeader.put("Link", Arrays.asList("<https://example.com/tos.pdf>; rel=\"terms-of-service\""));
+        linkHeader.put("Link", singletonList("<https://example.com/tos.pdf>; rel=\"terms-of-service\""));
 
         when(mockUrlConnection.getHeaderField("Content-Type")).thenReturn("application/problem+json");
         when(mockUrlConnection.getContentLength()).thenReturn(jsonData.length());
         when(mockUrlConnection.getHeaderFields()).thenReturn(linkHeader);
         when(mockUrlConnection.getResponseCode()).thenReturn(HttpURLConnection.HTTP_FORBIDDEN);
         when(mockUrlConnection.getOutputStream()).thenReturn(new ByteArrayOutputStream());
-        when(mockUrlConnection.getErrorStream()).thenReturn(new ByteArrayInputStream(jsonData.getBytes("utf-8")));
+        when(mockUrlConnection.getErrorStream()).thenReturn(new ByteArrayInputStream(jsonData.getBytes(UTF_8)));
         when(mockUrlConnection.getURL()).thenReturn(url("https://example.com/acme/1"));
 
         session.setNonce(TestUtils.DUMMY_NONCE);
@@ -510,7 +510,7 @@ public class DefaultConnectionTest {
         String jsonData = "{\"type\":\"urn:ietf:params:acme:error:rateLimited\",\"detail\":\"Too many invocations\"}";
 
         Map<String, List<String>> linkHeader = new HashMap<>();
-        linkHeader.put("Link", Arrays.asList("<https://example.com/rates.pdf>; rel=\"help\""));
+        linkHeader.put("Link", singletonList("<https://example.com/rates.pdf>; rel=\"help\""));
 
         Instant retryAfter = Instant.now().plusSeconds(30L).truncatedTo(ChronoUnit.MILLIS);
 
@@ -521,7 +521,7 @@ public class DefaultConnectionTest {
         when(mockUrlConnection.getHeaderFields()).thenReturn(linkHeader);
         when(mockUrlConnection.getResponseCode()).thenReturn(HttpURLConnection.HTTP_FORBIDDEN);
         when(mockUrlConnection.getOutputStream()).thenReturn(new ByteArrayOutputStream());
-        when(mockUrlConnection.getErrorStream()).thenReturn(new ByteArrayInputStream(jsonData.getBytes("utf-8")));
+        when(mockUrlConnection.getErrorStream()).thenReturn(new ByteArrayInputStream(jsonData.getBytes(UTF_8)));
         when(mockUrlConnection.getURL()).thenReturn(url("https://example.com/acme/1"));
 
         session.setNonce(TestUtils.DUMMY_NONCE);
@@ -762,7 +762,7 @@ public class DefaultConnectionTest {
         verify(mockUrlConnection, atLeast(0)).getHeaderFields();
         verifyNoMoreInteractions(mockUrlConnection);
 
-        JSON data = JSON.parse(new String(outputStream.toByteArray(), "utf-8"));
+        JSON data = JSON.parse(new String(outputStream.toByteArray(), UTF_8));
         String encodedHeader = data.get("protected").asString();
         String encodedSignature = data.get("signature").asString();
         String encodedPayload = data.get("payload").asString();
@@ -835,7 +835,7 @@ public class DefaultConnectionTest {
         verify(mockUrlConnection, atLeast(0)).getHeaderFields();
         verifyNoMoreInteractions(mockUrlConnection);
 
-        JSON data = JSON.parse(new String(outputStream.toByteArray(), "utf-8"));
+        JSON data = JSON.parse(new String(outputStream.toByteArray(), UTF_8));
         String encodedHeader = data.get("protected").asString();
         String encodedSignature = data.get("signature").asString();
         String encodedPayload = data.get("payload").asString();
@@ -961,7 +961,7 @@ public class DefaultConnectionTest {
         verify(mockUrlConnection, atLeast(0)).getHeaderFields();
         verifyNoMoreInteractions(mockUrlConnection);
 
-        JSON data = JSON.parse(new String(outputStream.toByteArray(), "utf-8"));
+        JSON data = JSON.parse(new String(outputStream.toByteArray(), UTF_8));
         String encodedHeader = data.get("protected").asString();
         String encodedSignature = data.get("signature").asString();
         String encodedPayload = data.get("payload").asString();
@@ -1013,7 +1013,7 @@ public class DefaultConnectionTest {
         when(mockUrlConnection.getHeaderField("Content-Type")).thenReturn("application/json");
         when(mockUrlConnection.getContentLength()).thenReturn(jsonData.length());
         when(mockUrlConnection.getResponseCode()).thenReturn(HttpURLConnection.HTTP_OK);
-        when(mockUrlConnection.getInputStream()).thenReturn(new ByteArrayInputStream(jsonData.getBytes("utf-8")));
+        when(mockUrlConnection.getInputStream()).thenReturn(new ByteArrayInputStream(jsonData.getBytes(UTF_8)));
 
         try (DefaultConnection conn = new DefaultConnection(mockHttpConnection)) {
             conn.conn = mockUrlConnection;
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/connector/HttpConnectorTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/connector/HttpConnectorTest.java
index e28cec04..952dc71c 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/connector/HttpConnectorTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/connector/HttpConnectorTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j.connector;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.verify;
 
@@ -37,7 +37,7 @@ public class HttpConnectorTest {
      * This is just a mock to check that the parameters are properly set.
      */
     @Test
-    public void testMockOpenConnection() throws IOException {
+    public void testMockOpenConnection() {
         NetworkSettings settings = new NetworkSettings();
         settings.setTimeout(Duration.ofSeconds(50));
 
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/connector/NetworkSettingsTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/connector/NetworkSettingsTest.java
index 03d92c55..c6aa35f3 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/connector/NetworkSettingsTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/connector/NetworkSettingsTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j.connector;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
-import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 
 import java.net.InetSocketAddress;
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/connector/ResourceIteratorTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/connector/ResourceIteratorTest.java
index c9904981..ad00bfeb 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/connector/ResourceIteratorTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/connector/ResourceIteratorTest.java
@@ -13,15 +13,14 @@
  */
 package org.shredzone.acme4j.connector;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 import static org.shredzone.acme4j.toolbox.TestUtils.url;
 
 import java.io.IOException;
 import java.net.HttpURLConnection;
 import java.net.URL;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Iterator;
@@ -41,12 +40,12 @@ import org.shredzone.acme4j.toolbox.JSONBuilder;
  */
 public class ResourceIteratorTest {
 
-    private final int PAGES = 4;
-    private final int RESOURCES_PER_PAGE = 5;
-    private final String TYPE = "authorizations";
+    private static final int PAGES = 4;
+    private static final int RESOURCES_PER_PAGE = 5;
+    private static final String TYPE = "authorizations";
 
-    private List<URL> resourceURLs = new ArrayList<>(PAGES * RESOURCES_PER_PAGE);
-    private List<URL> pageURLs = new ArrayList<>(PAGES);
+    private final List<URL> resourceURLs = new ArrayList<>(PAGES * RESOURCES_PER_PAGE);
+    private final List<URL> pageURLs = new ArrayList<>(PAGES);
 
     @Before
     public void setup() {
@@ -154,7 +153,7 @@ public class ResourceIteratorTest {
             @Override
             public Collection<URL> getLinks(String relation) {
                 if ("next".equals(relation) && (ix + 1 < pageURLs.size())) {
-                    return Arrays.asList(pageURLs.get(ix + 1));
+                    return Collections.singletonList(pageURLs.get(ix + 1));
                 }
                 return Collections.emptyList();
             }
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/connector/ResourceTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/connector/ResourceTest.java
index 4cc78024..c47328fe 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/connector/ResourceTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/connector/ResourceTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j.connector;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
-import static org.junit.Assert.assertThat;
 
 import org.junit.Test;
 
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/connector/SessionProviderTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/connector/SessionProviderTest.java
index 014a8579..68190827 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/connector/SessionProviderTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/connector/SessionProviderTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j.connector;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 
 import java.net.URI;
 import java.net.URL;
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/connector/TrimmingInputStreamTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/connector/TrimmingInputStreamTest.java
index a38228d4..d57fa9fb 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/connector/TrimmingInputStreamTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/connector/TrimmingInputStreamTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j.connector;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
-import static org.junit.Assert.assertThat;
 
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeExceptionTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeExceptionTest.java
index ce6c825e..85910055 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeExceptionTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeExceptionTest.java
@@ -13,9 +13,9 @@
  */
 package org.shredzone.acme4j.exception;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.nullValue;
-import static org.junit.Assert.assertThat;
 
 import java.io.IOException;
 
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeLazyLoadingExceptionTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeLazyLoadingExceptionTest.java
index 7d642ac5..e2fcf455 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeLazyLoadingExceptionTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeLazyLoadingExceptionTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j.exception;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 import static org.mockito.Mockito.mock;
 
 import java.net.URL;
@@ -29,7 +29,7 @@ import org.shredzone.acme4j.toolbox.TestUtils;
  */
 public class AcmeLazyLoadingExceptionTest {
 
-    private URL resourceUrl = TestUtils.url("http://example.com/acme/resource/123");
+    private final URL resourceUrl = TestUtils.url("http://example.com/acme/resource/123");
 
     @Test
     public void testAcmeLazyLoadingException() {
@@ -42,7 +42,7 @@ public class AcmeLazyLoadingExceptionTest {
         assertThat(ex, is(instanceOf(RuntimeException.class)));
         assertThat(ex.getMessage(), containsString(resourceUrl.toString()));
         assertThat(ex.getMessage(), containsString(TestResource.class.getSimpleName()));
-        assertThat(ex.getCause(), is((Throwable) cause));
+        assertThat(ex.getCause(), is(cause));
         assertThat(ex.getType(), is(equalTo(TestResource.class)));
         assertThat(ex.getLocation(), is(resourceUrl));
     }
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeNetworkExceptionTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeNetworkExceptionTest.java
index be6c7ba9..c58ea9af 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeNetworkExceptionTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeNetworkExceptionTest.java
@@ -13,9 +13,9 @@
  */
 package org.shredzone.acme4j.exception;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.notNullValue;
-import static org.junit.Assert.assertThat;
 
 import java.io.IOException;
 
@@ -33,7 +33,7 @@ public class AcmeNetworkExceptionTest {
         AcmeNetworkException ex = new AcmeNetworkException(cause);
 
         assertThat(ex.getMessage(), notNullValue());
-        assertThat(ex.getCause(), is((Throwable) cause));
+        assertThat(ex.getCause(), is(cause));
     }
 
 }
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeProtocolExceptionTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeProtocolExceptionTest.java
index c29aa0eb..3c89cb64 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeProtocolExceptionTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeProtocolExceptionTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j.exception;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 
 import org.junit.Test;
 
@@ -38,7 +38,7 @@ public class AcmeProtocolExceptionTest {
         NumberFormatException cause = new NumberFormatException("Not a number: abc");
         AcmeProtocolException ex = new AcmeProtocolException(message, cause);
         assertThat(ex.getMessage(), is(message));
-        assertThat(ex.getCause(), is((Throwable) cause));
+        assertThat(ex.getCause(), is(cause));
     }
 
 }
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeRateLimitedExceptionTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeRateLimitedExceptionTest.java
index 94cbe9cb..31b0d531 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeRateLimitedExceptionTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeRateLimitedExceptionTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j.exception;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 import static org.shredzone.acme4j.toolbox.TestUtils.createProblem;
 import static org.shredzone.acme4j.toolbox.TestUtils.url;
 
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeRetryAfterExceptionTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeRetryAfterExceptionTest.java
index 90752226..67c39758 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeRetryAfterExceptionTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeRetryAfterExceptionTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j.exception;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
-import static org.junit.Assert.assertThat;
 
 import java.time.Duration;
 import java.time.Instant;
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeUserActionRequiredExceptionTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeUserActionRequiredExceptionTest.java
index 3ff7b7ba..bde92479 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeUserActionRequiredExceptionTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeUserActionRequiredExceptionTest.java
@@ -13,9 +13,9 @@
  */
 package org.shredzone.acme4j.exception;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.nullValue;
-import static org.junit.Assert.assertThat;
 import static org.shredzone.acme4j.toolbox.TestUtils.createProblem;
 
 import java.net.MalformedURLException;
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/provider/AbstractAcmeProviderTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/provider/AbstractAcmeProviderTest.java
index da4dd57c..029a932b 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/provider/AbstractAcmeProviderTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/provider/AbstractAcmeProviderTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j.provider;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 import static org.mockito.Mockito.any;
 import static org.mockito.Mockito.*;
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/provider/GenericAcmeProviderTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/provider/GenericAcmeProviderTest.java
index c75a685c..bf01a64c 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/provider/GenericAcmeProviderTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/provider/GenericAcmeProviderTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j.provider;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 
 import java.net.URI;
 import java.net.URISyntaxException;
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/provider/letsencrypt/LetsEncryptAcmeProviderTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/provider/letsencrypt/LetsEncryptAcmeProviderTest.java
index 6685e4e7..f541142a 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/provider/letsencrypt/LetsEncryptAcmeProviderTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/provider/letsencrypt/LetsEncryptAcmeProviderTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j.provider.letsencrypt;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
-import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 import static org.shredzone.acme4j.toolbox.TestUtils.url;
 
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/provider/pebble/PebbleAcmeProviderTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/provider/pebble/PebbleAcmeProviderTest.java
index a73ca4d6..88518856 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/provider/pebble/PebbleAcmeProviderTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/provider/pebble/PebbleAcmeProviderTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j.provider.pebble;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
-import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 import static org.shredzone.acme4j.toolbox.TestUtils.url;
 
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/toolbox/AcmeUtilsTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/toolbox/AcmeUtilsTest.java
index cc60cb0d..a73a8382 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/toolbox/AcmeUtilsTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/toolbox/AcmeUtilsTest.java
@@ -13,9 +13,9 @@
  */
 package org.shredzone.acme4j.toolbox;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.nullValue;
-import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 import static org.shredzone.acme4j.toolbox.AcmeUtils.*;
 
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/toolbox/JSONBuilderTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/toolbox/JSONBuilderTest.java
index a357c7d0..c4e1acb3 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/toolbox/JSONBuilderTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/toolbox/JSONBuilderTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j.toolbox;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 
 import java.io.IOException;
 import java.security.KeyPair;
@@ -67,7 +67,7 @@ public class JSONBuilderTest {
         Map<String, Object> map = cb.toMap();
         assertThat(map.keySet(), hasSize(2));
         assertThat(map, allOf(
-                hasEntry("fooInt", (Object) 456),
+                hasEntry("fooInt", 456),
                 hasEntry("fooStr", (Object) "String")
         ));
 
@@ -161,7 +161,7 @@ public class JSONBuilderTest {
         assertThat(cb1.toString(), is("{\"ar\":[]}"));
 
         JSONBuilder cb2 = new JSONBuilder();
-        res = cb2.array("ar", Arrays.asList(123));
+        res = cb2.array("ar", Collections.singletonList(123));
         assertThat(res, is(sameInstance(cb2)));
         assertThat(cb2.toString(), is("{\"ar\":[123]}"));
 
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/toolbox/JSONTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/toolbox/JSONTest.java
index 4e312971..9a0dd201 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/toolbox/JSONTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/toolbox/JSONTest.java
@@ -13,8 +13,9 @@
  */
 package org.shredzone.acme4j.toolbox;
 
+import static java.nio.charset.StandardCharsets.UTF_8;
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 import static org.shredzone.acme4j.toolbox.TestUtils.url;
 import static uk.co.datumedge.hamcrest.json.SameJSONAs.sameJSONAs;
@@ -25,7 +26,6 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
-import java.net.MalformedURLException;
 import java.net.URI;
 import java.net.URL;
 import java.time.Duration;
@@ -77,7 +77,7 @@ public class JSONTest {
         assertThat(map.get("foo"), is("a-text"));
         assertThat(map.get("bar"), is(123L));
 
-        try (InputStream in = new ByteArrayInputStream(json.getBytes("utf-8"))) {
+        try (InputStream in = new ByteArrayInputStream(json.getBytes(UTF_8))) {
             JSON fromStream = JSON.parse(in);
             assertThat(fromStream.toString(), is(sameJSONAs(json)));
             Map<String, Object> map2 = fromStream.toMap();
@@ -92,7 +92,7 @@ public class JSONTest {
      * Test that bad JSON fails.
      */
     @Test(expected = AcmeProtocolException.class)
-    public void testParsersBadJSON() throws IOException {
+    public void testParsersBadJSON() {
         JSON.parse("This is no JSON.");
     }
 
@@ -247,7 +247,7 @@ public class JSONTest {
      * Test that getters are null safe.
      */
     @Test
-    public void testNullGetter() throws MalformedURLException {
+    public void testNullGetter() {
         JSON json = TestUtils.getJSON("datatypes");
 
         assertThat(json.get("none"), is(notNullValue()));
@@ -344,7 +344,7 @@ public class JSONTest {
      * Test that wrong getters return an exception.
      */
     @Test
-    public void testWrongGetter() throws MalformedURLException {
+    public void testWrongGetter() {
         JSON json = TestUtils.getJSON("datatypes");
 
         try {
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/toolbox/JoseUtilsTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/toolbox/JoseUtilsTest.java
index 88600a55..2a09ce50 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/toolbox/JoseUtilsTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/toolbox/JoseUtilsTest.java
@@ -14,8 +14,8 @@
 package org.shredzone.acme4j.toolbox;
 
 import static java.nio.charset.StandardCharsets.UTF_8;
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 import static org.shredzone.acme4j.toolbox.TestUtils.url;
 import static uk.co.datumedge.hamcrest.json.SameJSONAs.sameJSONAs;
diff --git a/acme4j-it/src/test/java/org/shredzone/acme4j/it/boulder/OrderHttpIT.java b/acme4j-it/src/test/java/org/shredzone/acme4j/it/boulder/OrderHttpIT.java
index 476aab3b..0b44e763 100644
--- a/acme4j-it/src/test/java/org/shredzone/acme4j/it/boulder/OrderHttpIT.java
+++ b/acme4j-it/src/test/java/org/shredzone/acme4j/it/boulder/OrderHttpIT.java
@@ -15,8 +15,9 @@ package org.shredzone.acme4j.it.boulder;
 
 import static java.util.concurrent.TimeUnit.SECONDS;
 import static org.awaitility.Awaitility.await;
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.*;
+import static org.junit.Assert.fail;
 
 import java.net.URI;
 import java.security.KeyPair;
@@ -46,7 +47,7 @@ public class OrderHttpIT {
 
     private final String bammbammUrl = System.getProperty("bammbammUrl", "http://localhost:14001");
 
-    private BammBammClient client = new BammBammClient(bammbammUrl);
+    private final BammBammClient client = new BammBammClient(bammbammUrl);
 
     /**
      * Test if a certificate can be ordered via http-01 challenge.
diff --git a/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/AccountIT.java b/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/AccountIT.java
index 81f98370..11d22f6f 100644
--- a/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/AccountIT.java
+++ b/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/AccountIT.java
@@ -13,8 +13,10 @@
  */
 package org.shredzone.acme4j.it.pebble;
 
-import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.*;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.contains;
+import static org.hamcrest.Matchers.is;
+import static org.junit.Assert.fail;
 
 import java.net.URI;
 import java.net.URL;
diff --git a/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/OrderIT.java b/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/OrderIT.java
index 00b9564c..2226e810 100644
--- a/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/OrderIT.java
+++ b/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/OrderIT.java
@@ -15,8 +15,9 @@ package org.shredzone.acme4j.it.pebble;
 
 import static java.util.concurrent.TimeUnit.SECONDS;
 import static org.awaitility.Awaitility.await;
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.*;
+import static org.junit.Assert.fail;
 
 import java.net.URI;
 import java.security.KeyPair;
@@ -154,7 +155,7 @@ public class OrderIT extends PebbleITBase {
 
         KeyPair domainKeyPair = createKeyPair();
 
-        Instant notBefore = Instant.now().truncatedTo(ChronoUnit.MILLIS);
+        Instant notBefore = Instant.now().truncatedTo(ChronoUnit.SECONDS);
         Instant notAfter = notBefore.plus(Duration.ofDays(20L));
 
         Order order = account.newOrder()
@@ -208,8 +209,8 @@ public class OrderIT extends PebbleITBase {
         Certificate certificate = order.getCertificate();
         X509Certificate cert = certificate.getCertificate();
         assertThat(cert, not(nullValue()));
-        assertThat(cert.getNotAfter(), not(nullValue()));
-        assertThat(cert.getNotBefore(), not(nullValue()));
+        assertThat(cert.getNotBefore().toInstant(), is(notNullValue()));
+        assertThat(cert.getNotAfter().toInstant(), is(notNullValue()));
         assertThat(cert.getSubjectX500Principal().getName(), containsString("CN=" + domain));
 
         for (Authorization auth :  order.getAuthorizations()) {
@@ -260,12 +261,12 @@ public class OrderIT extends PebbleITBase {
     }
 
     @FunctionalInterface
-    private static interface Validator {
+    private interface Validator {
         Challenge prepare(Authorization auth) throws Exception;
     }
 
     @FunctionalInterface
-    private static interface Revoker {
+    private interface Revoker {
         void revoke(Session session, Certificate certificate, KeyPair keyPair,
             KeyPair domainKeyPair) throws Exception;
     }
diff --git a/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/OrderWildcardIT.java b/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/OrderWildcardIT.java
index 1e21adc2..0cc3d001 100644
--- a/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/OrderWildcardIT.java
+++ b/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/OrderWildcardIT.java
@@ -16,8 +16,9 @@ package org.shredzone.acme4j.it.pebble;
 import static java.util.concurrent.TimeUnit.SECONDS;
 import static java.util.stream.Collectors.toList;
 import static org.awaitility.Awaitility.await;
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.*;
+import static org.junit.Assert.fail;
 
 import java.security.KeyPair;
 import java.security.cert.X509Certificate;
diff --git a/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/PebbleITBase.java b/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/PebbleITBase.java
index d2caf5ce..30f99888 100644
--- a/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/PebbleITBase.java
+++ b/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/PebbleITBase.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j.it.pebble;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 
 import java.net.URI;
 import java.net.URL;
@@ -133,7 +133,7 @@ public abstract class PebbleITBase {
     }
 
     @FunctionalInterface
-    public static interface CleanupCallback {
+    public interface CleanupCallback {
         void cleanup() throws Exception;
     }
 
diff --git a/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/SessionIT.java b/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/SessionIT.java
index f22ef4aa..1baef4dd 100644
--- a/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/SessionIT.java
+++ b/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/SessionIT.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j.it.pebble;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 import static uk.co.datumedge.hamcrest.json.SameJSONAs.sameJSONAs;
 
 import java.net.URI;
diff --git a/acme4j-utils/src/test/java/org/shredzone/acme4j/util/CertificateUtilsTest.java b/acme4j-utils/src/test/java/org/shredzone/acme4j/util/CertificateUtilsTest.java
index 9d43e9e0..095cbf9b 100644
--- a/acme4j-utils/src/test/java/org/shredzone/acme4j/util/CertificateUtilsTest.java
+++ b/acme4j-utils/src/test/java/org/shredzone/acme4j/util/CertificateUtilsTest.java
@@ -14,8 +14,8 @@
 package org.shredzone.acme4j.util;
 
 import static java.time.temporal.ChronoUnit.SECONDS;
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
diff --git a/acme4j-utils/src/test/java/org/shredzone/acme4j/util/KeyPairUtilsTest.java b/acme4j-utils/src/test/java/org/shredzone/acme4j/util/KeyPairUtilsTest.java
index f6005925..ff14b144 100644
--- a/acme4j-utils/src/test/java/org/shredzone/acme4j/util/KeyPairUtilsTest.java
+++ b/acme4j-utils/src/test/java/org/shredzone/acme4j/util/KeyPairUtilsTest.java
@@ -13,8 +13,8 @@
  */
 package org.shredzone.acme4j.util;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.assertThat;
 
 import java.io.IOException;
 import java.io.StringReader;