Add test for `isValidResolvConf` (#10302)

Signed-off-by: Francisco <francisco.moral@suse.com>

pkg/agent/config/config_internal_test.go

@@ -0,0 +1,40 @@
+package config
+
+import (
+	"os"
+	"testing"
+)
+
+func Test_isValidResolvConf(t *testing.T) {
+	tests := []struct {
+		name           string
+		fileContent    string
+		expectedResult bool
+	}{
+		{name: "Valid ResolvConf", fileContent: "nameserver 8.8.8.8\nnameserver 2001:4860:4860::8888\n", expectedResult: true},
+		{name: "Invalid ResolvConf", fileContent: "nameserver 999.999.999.999\nnameserver not.an.ip\n", expectedResult: false},
+		{name: "Wrong Nameserver", fileContent: "search example.com\n", expectedResult: false},
+		{name: "One valid nameserver", fileContent: "test test.com\nnameserver 8.8.8.8", expectedResult: true},
+		{name: "Non GlobalUnicast", fileContent: "nameserver ::1\nnameserver 169.254.0.1\nnameserver fe80::1\n", expectedResult: false},
+		{name: "Empty File", fileContent: "", expectedResult: false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			tmpfile, err := os.CreateTemp("", "resolv.conf")
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer os.Remove(tmpfile.Name())
+
+			if _, err := tmpfile.WriteString(tt.fileContent); err != nil {
+				t.Errorf("error writing to file: %v with content: %v", tmpfile.Name(), tt.fileContent)
+			}
+
+			res := isValidResolvConf(tmpfile.Name())
+			if res != tt.expectedResult {
+				t.Errorf("isValidResolvConf(%s) = %v; want %v", tt.name, res, tt.expectedResult)
+			}
+		})
+	}
+}