Merge pull request #15357 from sam-gardner/BAEL-7240-Verify-Lambda-call-using-mockito

BAEL-7240 Add example code for verifying lambda calls with mockito

testing-modules/mockito-2/src/main/java/com/baeldung/lambdacalls/LambdaExample.java

@@ -0,0 +1,26 @@
+package com.baeldung.lambdacalls;
+
+import java.util.ArrayList;
+
+public class LambdaExample {
+
+    private BrickLayer brickLayer = new BrickLayer();
+
+    static ArrayList<String> bricksList = new ArrayList<>();
+
+    public void createWall(String bricks){
+        Runnable build = () -> brickLayer.layBricks(bricks);
+        build.run();
+    }
+
+    public ArrayList<String> getBricksList(){
+        return bricksList;
+    }
+
+    static class BrickLayer {
+        void layBricks(String bricks){
+            bricksList.add(bricks);
+        }
+    }
+
+}

testing-modules/mockito-2/src/test/java/com/baeldung/lambdacalls/LambdaCallsUnitTest.java

@@ -0,0 +1,41 @@
+package com.baeldung.lambdacalls;
+
+import static com.baeldung.lambdacalls.LambdaExample.*;
+import static junit.framework.TestCase.assertEquals;
+import static org.mockito.Mockito.verify;
+
+import java.util.ArrayList;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.InjectMocks;
+import org.mockito.Mock;
+import org.mockito.junit.MockitoJUnitRunner;
+
+@RunWith(MockitoJUnitRunner.class)
+public class LambdaCallsUnitTest {
+
+    @Mock
+    private/**/ BrickLayer brickLayer;
+    @InjectMocks
+    private LambdaExample lambdaExample;
+
+    @Test
+    public void whenCallingALambda_thenTheInvocationCanBeConfirmedWithCorrectArguments(){
+        String bricks = "red bricks";
+        lambdaExample.createWall(bricks);
+        verify(brickLayer).layBricks(bricks);
+    }
+
+    @Test
+    public void whenCallingALambda_thenCorrectBehaviourIsPerformed(){
+        LambdaExample lambdaExample = new LambdaExample();
+        String bricks = "red bricks";
+
+        lambdaExample.createWall(bricks);
+        ArrayList<String> bricksList = lambdaExample.getBricksList();
+
+        assertEquals(bricks, bricksList.get(0));
+    }
+
+}