BAEL-2512 - Add a new section in Mockito Spy article

testing-modules/mockito/src/test/java/org/baeldung/mockito/misusing/MockitoMisusingUnitTest.java

@@ -0,0 +1,30 @@
+package org.baeldung.mockito.misusing;
+
+import static org.hamcrest.core.StringContains.containsString;
+import static org.junit.Assert.assertThat;
+import static org.junit.Assert.fail;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.junit.Test;
+import org.mockito.Mockito;
+import org.mockito.exceptions.misusing.NotAMockException;
+
+public class MockitoMisusingUnitTest {
+
+    @Test
+    public void givenNotASpy_whenDoReturn_thenThrowNotAMock() {
+        try {
+            List<String> list = new ArrayList<String>();
+            Mockito.doReturn(100)
+                .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!"));
+        }
+    }
+
+}