diff --git a/testing-modules/mockito-simple/src/test/java/com/baeldung/mockito/spy/MockitoMisusingMockOrSpyUnitTest.java b/testing-modules/mockito-simple/src/test/java/com/baeldung/mockito/spy/MockitoMisusingMockOrSpyUnitTest.java
new file mode 100644
index 0000000000..b3f470427a
--- /dev/null
+++ b/testing-modules/mockito-simple/src/test/java/com/baeldung/mockito/spy/MockitoMisusingMockOrSpyUnitTest.java
@@ -0,0 +1,30 @@
+package com.baeldung.mockito.spy;
+
+import static org.assertj.core.api.Assertions.assertThatNoException;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.junit.Test;
+import org.mockito.Mockito;
+import org.mockito.exceptions.misusing.NotAMockException;
+
+public class MockitoMisusingMockOrSpyUnitTest {
+
+    @Test
+    public void givenNotASpy_whenDoReturn_thenThrowNotAMock() {
+        List<String> list = new ArrayList<String>();
+
+        assertThatThrownBy(() -> Mockito.doReturn(100).when(list).size())
+            .isInstanceOf(NotAMockException.class)
+            .hasMessageContaining("Argument passed to when() is not a mock!");
+    }
+    
+    @Test
+    public void givenASpy_whenDoReturn_thenNoError() {
+        final List<String> spyList = Mockito.spy(new ArrayList<>());
+        
+        assertThatNoException().isThrownBy(() -> Mockito.doReturn(100).when(spyList).size());
+    }
+}
diff --git a/testing-modules/mockito-simple/src/test/java/com/baeldung/mockito/spy/MockitoMisusingUnitTest.java b/testing-modules/mockito-simple/src/test/java/com/baeldung/mockito/spy/MockitoMisusingUnitTest.java
deleted file mode 100644
index ea12061fc6..0000000000
--- a/testing-modules/mockito-simple/src/test/java/com/baeldung/mockito/spy/MockitoMisusingUnitTest.java
+++ /dev/null
@@ -1,38 +0,0 @@
-package com.baeldung.mockito.spy;
-
-import org.junit.After;
-import org.junit.Test;
-import org.mockito.Mockito;
-import org.mockito.exceptions.misusing.NotAMockException;
-import org.mockito.internal.progress.ThreadSafeMockingProgress;
-
-import java.util.ArrayList;
-import java.util.List;
-
-import static org.hamcrest.CoreMatchers.containsString;
-import static org.junit.Assert.assertThat;
-import static org.junit.jupiter.api.Assertions.fail;
-
-public class MockitoMisusingUnitTest {
-
-    @After
-    public void tearDown() {
-        ThreadSafeMockingProgress.mockingProgress().reset();
-    }
-    
-    @Test
-    public void givenNotASpy_whenDoReturn_thenThrowNotAMock() {
-        try {
-            List<String> list = new ArrayList<String>();
-
-            Mockito.doReturn(100, Mockito.withSettings().lenient())
-                .when(list)
-                .size();
-
-            fail("Should have thrown a NotAMockException because 'list' is not a mock!");
-        } catch (NotAMockException e) {
-            assertThat(e.getMessage(), containsString("Argument passed to when() is not a mock!"));
-        }
-    }
-
-}
diff --git a/testing-modules/mockito-simple/src/test/java/com/baeldung/mockito/spy/MockitoSpyUnitTest.java b/testing-modules/mockito-simple/src/test/java/com/baeldung/mockito/spy/MockitoSpyUnitTest.java
index d4696e482b..28ca0c327b 100644
--- a/testing-modules/mockito-simple/src/test/java/com/baeldung/mockito/spy/MockitoSpyUnitTest.java
+++ b/testing-modules/mockito-simple/src/test/java/com/baeldung/mockito/spy/MockitoSpyUnitTest.java
@@ -1,22 +1,20 @@
 package com.baeldung.mockito.spy;
 
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.Assert.assertEquals;
+
+import java.util.ArrayList;
+import java.util.List;
+
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mockito.Mockito;
 import org.mockito.Spy;
 import org.mockito.junit.MockitoJUnitRunner;
 
-import java.util.ArrayList;
-import java.util.List;
-
-import static org.junit.Assert.assertEquals;
-
 @RunWith(MockitoJUnitRunner.class)
 public class MockitoSpyUnitTest {
 
-    @Spy
-    private List<String> aSpyList = new ArrayList<String>();
-
     @Test
     public void whenSpyingOnList_thenCorrect() {
         final List<String> list = new ArrayList<String>();
@@ -28,9 +26,12 @@ public class MockitoSpyUnitTest {
         Mockito.verify(spyList).add("one");
         Mockito.verify(spyList).add("two");
 
-        assertEquals(2, spyList.size());
+        assertThat(spyList).hasSize(2);
     }
 
+    @Spy
+    private List<String> aSpyList = new ArrayList<String>();
+
     @Test
     public void whenUsingTheSpyAnnotation_thenObjectIsSpied() {
         aSpyList.add("one");
@@ -39,7 +40,7 @@ public class MockitoSpyUnitTest {
         Mockito.verify(aSpyList).add("one");
         Mockito.verify(aSpyList).add("two");
 
-        assertEquals(2, aSpyList.size());
+        assertThat(aSpyList).hasSize(2);
     }
 
     @Test
@@ -50,7 +51,7 @@ public class MockitoSpyUnitTest {
         assertEquals(0, spyList.size());
 
         Mockito.doReturn(100).when(spyList).size();
-        assertEquals(100, spyList.size());
+        assertThat(spyList).hasSize(100);
     }
 
     @Test
@@ -60,17 +61,17 @@ public class MockitoSpyUnitTest {
         mockedList.add("one");
         Mockito.verify(mockedList).add("one");
 
-        assertEquals(0, mockedList.size());
+        assertThat(mockedList).hasSize(0);
     }
 
     @Test
     public void whenCreateSpy_thenCreate() {
-        final List<String> spyList = Mockito.spy(new ArrayList<String>());
+        final List<String> spyList = Mockito.spy(new ArrayList<>());
 
         spyList.add("one");
         Mockito.verify(spyList).add("one");
 
-        assertEquals(1, spyList.size());
+        assertThat(spyList).hasSize(1);
     }
 
 }