diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/RegistrationTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/RegistrationTest.java
index d919d953..9e285a82 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/RegistrationTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/RegistrationTest.java
@@ -35,6 +35,7 @@ import org.jose4j.jws.JsonWebSignature;
 import org.jose4j.jwx.CompactSerializer;
 import org.jose4j.lang.JoseException;
 import org.junit.Test;
+import org.shredzone.acme4j.Registration.EditableRegistration;
 import org.shredzone.acme4j.challenge.Challenge;
 import org.shredzone.acme4j.challenge.Dns01Challenge;
 import org.shredzone.acme4j.challenge.Http01Challenge;
@@ -261,6 +262,32 @@ public class RegistrationTest {
         provider.close();
     }
 
+    /**
+     * Test that a bad domain parameter is not accepted.
+     */
+    @Test
+    public void testAuthorizeBadDomain() throws Exception {
+        TestableConnectionProvider provider = new TestableConnectionProvider();
+        Session session = provider.createSession();
+        Registration registration = Registration.bind(session, locationUri);
+
+        try {
+            registration.authorizeDomain(null);
+            fail("null domain was accepted");
+        } catch (NullPointerException ex) {
+            // expected
+        }
+
+        try {
+            registration.authorizeDomain("");
+            fail("empty domain string was accepted");
+        } catch (IllegalArgumentException ex) {
+            // expected
+        }
+
+        provider.close();
+    }
+
     /**
      * Test that a certificate can be requested and is delivered synchronously.
      */
@@ -533,15 +560,19 @@ public class RegistrationTest {
 
         Registration registration = new Registration(provider.createSession(), locationUri);
 
-        registration.modify()
-                .setAgreement(agreementUri)
-                .addContact("mailto:foo2@example.com")
-                .commit();
+        EditableRegistration editable = registration.modify();
+        assertThat(editable, notNullValue());
+
+        editable.setAgreement(agreementUri);
+        editable.addContact("mailto:foo2@example.com");
+        editable.getContacts().add(URI.create("mailto:foo3@example.com"));
+        editable.commit();
 
         assertThat(registration.getLocation(), is(locationUri));
         assertThat(registration.getAgreement(), is(agreementUri));
-        assertThat(registration.getContacts().size(), is(1));
+        assertThat(registration.getContacts().size(), is(2));
         assertThat(registration.getContacts().get(0), is(URI.create("mailto:foo2@example.com")));
+        assertThat(registration.getContacts().get(1), is(URI.create("mailto:foo3@example.com")));
 
         provider.close();
     }
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 11040356..1ea88580 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
@@ -415,6 +415,32 @@ public class DefaultConnectionTest {
         verifyNoMoreInteractions(mockUrlConnection);
     }
 
+    /**
+     * Test if an {@link AcmeException} is thrown if there is a generic error.
+     */
+    @Test
+    public void testAcceptThrowsServerException() throws IOException {
+        when(mockUrlConnection.getHeaderField("Content-Type"))
+                .thenReturn("text/html");
+        when(mockUrlConnection.getResponseCode())
+                .thenReturn(HttpURLConnection.HTTP_INTERNAL_ERROR);
+        when(mockUrlConnection.getResponseMessage())
+                .thenReturn("Infernal Server Error");
+
+        try (DefaultConnection conn = new DefaultConnection(mockHttpConnection)) {
+            conn.conn = mockUrlConnection;
+            conn.accept(HttpURLConnection.HTTP_OK);
+            fail("Expected to fail");
+        } catch (AcmeException ex) {
+            assertThat(ex.getMessage(), is("HTTP 500: Infernal Server Error"));
+        }
+
+        verify(mockUrlConnection).getHeaderField("Content-Type");
+        verify(mockUrlConnection, atLeastOnce()).getResponseCode();
+        verify(mockUrlConnection, atLeastOnce()).getResponseMessage();
+        verifyNoMoreInteractions(mockUrlConnection);
+    }
+
     /**
      * Test GET requests.
      */
@@ -503,6 +529,17 @@ public class DefaultConnectionTest {
         assertThat(jws.verifySignature(), is(true));
     }
 
+    /**
+     * Test signed POST requests if there is no nonce.
+     */
+    @Test(expected = AcmeProtocolException.class)
+    public void testSendSignedRequestNoNonce() throws Exception {
+        try (DefaultConnection conn = new DefaultConnection(mockHttpConnection)) {
+            ClaimBuilder cb = new ClaimBuilder();
+            conn.sendSignedRequest(requestUri, cb, DefaultConnectionTest.this.session);
+        }
+    }
+
     /**
      * Test getting a JSON response.
      */
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
new file mode 100644
index 00000000..1fbad451
--- /dev/null
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeRetryAfterExceptionTest.java
@@ -0,0 +1,55 @@
+/*
+ * acme4j - Java ACME client
+ *
+ * Copyright (C) 2016 Richard "Shred" Körber
+ *   http://acme4j.shredzone.org
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ */
+package org.shredzone.acme4j.exception;
+
+import static org.hamcrest.Matchers.*;
+import static org.junit.Assert.assertThat;
+
+import java.util.Date;
+
+import org.junit.Test;
+
+/**
+ * Unit tests for {@link AcmeRetryAfterException}.
+ */
+public class AcmeRetryAfterExceptionTest {
+
+    /**
+     * Test that parameters are correctly returned.
+     */
+    @Test
+    public void testAcmeRetryAfterException() {
+        String detail = "Too early";
+        Date retryAfter = new Date(System.currentTimeMillis() + 60 * 1000L);
+
+        AcmeRetryAfterException ex
+                = new AcmeRetryAfterException(detail, retryAfter);
+
+        assertThat(ex.getMessage(), is(detail));
+        assertThat(ex.getRetryAfter(), is(retryAfter));
+    }
+
+    /**
+     * Test that optional parameters are null-safe.
+     */
+    @Test
+    public void testNullAcmeRetryAfterException() {
+        AcmeRetryAfterException ex
+                = new AcmeRetryAfterException(null, null);
+
+        assertThat(ex.getMessage(), nullValue());
+        assertThat(ex.getRetryAfter(), nullValue());
+    }
+
+}
diff --git a/acme4j-client/src/test/resources/json.properties b/acme4j-client/src/test/resources/json.properties
index 78b5fb2b..1eeaff6c 100644
--- a/acme4j-client/src/test/resources/json.properties
+++ b/acme4j-client/src/test/resources/json.properties
@@ -42,11 +42,11 @@ newRegistration = \
 modifyRegistration = \
   {"resource":"reg",\
    "agreement":"http://example.com/agreement.pdf",\
-   "contact":["mailto:foo2@example.com"]}
+   "contact":["mailto:foo2@example.com","mailto:foo3@example.com"]}
 
 modifyRegistrationResponse = \
   {"agreement":"http://example.com/agreement.pdf",\
-   "contact":["mailto:foo2@example.com"]}
+   "contact":["mailto:foo2@example.com","mailto:foo3@example.com"]}
 
 updateRegistration = \
   {"resource":"reg"}