diff --git a/src/main/java/io/github/brenoepics/at4j/util/logging/FallbackLoggerConfiguration.java b/src/main/java/io/github/brenoepics/at4j/util/logging/FallbackLoggerConfiguration.java
index 5697708b..903301f5 100644
--- a/src/main/java/io/github/brenoepics/at4j/util/logging/FallbackLoggerConfiguration.java
+++ b/src/main/java/io/github/brenoepics/at4j/util/logging/FallbackLoggerConfiguration.java
@@ -9,7 +9,8 @@ public class FallbackLoggerConfiguration {
 
   private static final AtomicBoolean trace = new AtomicBoolean();
 
-  private FallbackLoggerConfiguration() {
+  /** This class should not be instantiated. */
+  FallbackLoggerConfiguration() {
     throw new UnsupportedOperationException();
   }
 
diff --git a/src/test/java/io/github/brenoepics/at4j/core/exceptions/AzureExceptionTest.java b/src/test/java/io/github/brenoepics/at4j/core/exceptions/AzureExceptionTest.java
index 403c3b6b..b4bf0a7c 100644
--- a/src/test/java/io/github/brenoepics/at4j/core/exceptions/AzureExceptionTest.java
+++ b/src/test/java/io/github/brenoepics/at4j/core/exceptions/AzureExceptionTest.java
@@ -14,8 +14,8 @@
 import java.util.HashMap;
 import java.util.Optional;
 
-import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 class AzureExceptionTest<T> {
 
diff --git a/src/test/java/io/github/brenoepics/at4j/data/DetectedLanguageTest.java b/src/test/java/io/github/brenoepics/at4j/data/DetectedLanguageTest.java
index 949c95f9..bf4b933a 100644
--- a/src/test/java/io/github/brenoepics/at4j/data/DetectedLanguageTest.java
+++ b/src/test/java/io/github/brenoepics/at4j/data/DetectedLanguageTest.java
@@ -24,6 +24,18 @@ void ofJSON_withValidJson_returnsDetectedLanguage() throws JsonProcessingExcepti
     assertFalse(detectedLanguage.isTransliterationSupported());
   }
 
+  @Test
+  void ofJSON_withInvalidLangJson_returnsNull() throws JsonProcessingException {
+    String json =
+        "{\"score\":0.9,\"isTranslationSupported\":true,\"isTransliterationSupported\":false}";
+    ObjectMapper mapper = new ObjectMapper();
+    ObjectNode jsonNode = mapper.convertValue(mapper.readTree(json), ObjectNode.class);
+
+    DetectedLanguage detectedLanguage = DetectedLanguage.ofJSON(jsonNode);
+
+    assertNull(detectedLanguage);
+  }
+
   @Test
   void ofJSON_withMissingFields_returnsDetectedLanguageWithDefaults()
       throws JsonProcessingException {
diff --git a/src/test/java/io/github/brenoepics/at4j/data/TranslationTest.java b/src/test/java/io/github/brenoepics/at4j/data/TranslationTest.java
new file mode 100644
index 00000000..89047e04
--- /dev/null
+++ b/src/test/java/io/github/brenoepics/at4j/data/TranslationTest.java
@@ -0,0 +1,49 @@
+package io.github.brenoepics.at4j.data;
+
+import com.fasterxml.jackson.databind.node.JsonNodeFactory;
+import com.fasterxml.jackson.databind.node.ObjectNode;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class TranslationTest {
+
+		@Test
+		void from_createsTranslationWithGivenParameters() {
+				Translation translation = Translation.from("en", "Hello");
+
+				assertEquals("en", translation.getLanguageCode());
+				assertEquals("Hello", translation.getText());
+		}
+
+		@Test
+		void ofJSON_createsTranslationFromValidNode() {
+				ObjectNode node = JsonNodeFactory.instance.objectNode();
+				node.put("to", "en");
+				node.put("text", "Hello");
+
+				Translation translation = Translation.ofJSON(node);
+
+				assertNotNull(translation);
+				assertEquals("en", translation.getLanguageCode());
+				assertEquals("Hello", translation.getText());
+		}
+
+		@Test
+		void ofJSON_returnsNullForInvalidNode() {
+				ObjectNode node = JsonNodeFactory.instance.objectNode();
+				node.put("invalid", "data");
+
+				Translation translation = Translation.ofJSON(node);
+
+				assertNull(translation);
+		}
+
+		@Test
+		void toString_returnsCorrectFormat() {
+				Translation translation = Translation.from("en", "Hello");
+
+				String expected = "Translation{key='en', value='Hello'}";
+				assertEquals(expected, translation.toString());
+		}
+}
\ No newline at end of file
diff --git a/src/test/java/io/github/brenoepics/at4j/util/logging/FallbackLoggerConfigurationTest.java b/src/test/java/io/github/brenoepics/at4j/util/logging/FallbackLoggerConfigurationTest.java
index a7f93d8a..db4745df 100644
--- a/src/test/java/io/github/brenoepics/at4j/util/logging/FallbackLoggerConfigurationTest.java
+++ b/src/test/java/io/github/brenoepics/at4j/util/logging/FallbackLoggerConfigurationTest.java
@@ -6,6 +6,10 @@
 
 class FallbackLoggerConfigurationTest {
 
+  @Test
+  void invokingConstructorThrowsException() {
+    assertThrows(UnsupportedOperationException.class, FallbackLoggerConfiguration::new);
+  }
   @Test
   void debugInitiallyEnabled() {
     assertTrue(FallbackLoggerConfiguration.isDebugEnabled());
diff --git a/src/test/java/io/github/brenoepics/at4j/util/rest/RestRequestResultErrorCodeTest.java b/src/test/java/io/github/brenoepics/at4j/util/rest/RestRequestResultErrorCodeTest.java
index 1e4de7b9..1f86ba72 100644
--- a/src/test/java/io/github/brenoepics/at4j/util/rest/RestRequestResultErrorCodeTest.java
+++ b/src/test/java/io/github/brenoepics/at4j/util/rest/RestRequestResultErrorCodeTest.java
@@ -1,7 +1,14 @@
 package io.github.brenoepics.at4j.util.rest;
 
+import com.google.common.collect.Multimaps;
+import io.github.brenoepics.at4j.AzureApi;
+import io.github.brenoepics.at4j.AzureApiBuilder;
+import io.github.brenoepics.at4j.core.exceptions.AzureException;
+import okhttp3.Protocol;
+import okhttp3.Response;
 import org.junit.jupiter.api.Test;
 
+import java.io.IOException;
 import java.util.Arrays;
 import java.util.HashMap;
 import java.util.Map;
@@ -9,7 +16,7 @@
 
 import static org.junit.jupiter.api.Assertions.*;
 
-class RestRequestResultErrorCodeTest {
+class RestRequestResultErrorCodeTest<T> {
 
   @Test
   void test_all_enum_values() {