Mocking and verification of private methods using PowerMock (#2756)

mockito/src/test/java/com/baeldung/powermockito/introduction/LuckyNumberGenerator.java

@@ -0,0 +1,27 @@
+package com.baeldung.powermockito.introduction;
+
+class LuckyNumberGenerator {
+
+    public int getLuckyNumber(String name) {
+
+        record(name);
+
+        if (name == null) {
+            return getDefaultLuckyNumber();
+        }
+
+        return getLuckyNumber(name.length() + 1);
+    }
+
+    private void record(String name) {
+    }
+
+    private int getDefaultLuckyNumber() {
+        return 100;
+    }
+
+    private int getLuckyNumber(int length) {
+        return length < 5 ? 5 : 10000;
+    }
+
+}

mockito/src/test/java/com/baeldung/powermockito/introduction/LuckyNumberGeneratorTest.java

@@ -0,0 +1,51 @@
+package com.baeldung.powermockito.introduction;
+
+import static org.junit.Assert.assertEquals;
+import static org.powermock.api.mockito.PowerMockito.doReturn;
+import static org.powermock.api.mockito.PowerMockito.spy;
+import static org.powermock.api.mockito.PowerMockito.verifyPrivate;
+import static org.powermock.api.mockito.PowerMockito.when;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.ArgumentMatchers;
+import org.powermock.core.classloader.annotations.PrepareForTest;
+import org.powermock.modules.junit4.PowerMockRunner;
+
+@RunWith(PowerMockRunner.class)
+@PrepareForTest(fullyQualifiedNames = "com.baeldung.powermockito.introduction.LuckyNumberGenerator")
+public class LuckyNumberGeneratorTest {
+
+    @Test
+    public final void givenPrivateMethodWithReturn_whenUsingPowerMockito_thenCorrect() throws Exception {
+        LuckyNumberGenerator mock = spy(new LuckyNumberGenerator());
+
+        when(mock, "getDefaultLuckyNumber").thenReturn(300);
+
+        int result = mock.getLuckyNumber(null);
+
+        assertEquals(300, result);
+    }
+
+    @Test
+    public final void givenPrivateMethodWithArgumentAndReturn_whenUsingPowerMockito_thenCorrect() throws Exception {
+        LuckyNumberGenerator mock = spy(new LuckyNumberGenerator());
+
+        doReturn(1).when(mock, "getLuckyNumber", ArgumentMatchers.anyInt());
+
+        int result = mock.getLuckyNumber("Jack");
+
+        assertEquals(1, result);
+    }
+
+    @Test
+    public final void givenPrivateMethodWithNoArgumentAndReturn_whenUsingPowerMockito_thenCorrect() throws Exception {
+        LuckyNumberGenerator mock = spy(new LuckyNumberGenerator());
+
+        int result = mock.getLuckyNumber("Tyranosorous");
+
+        verifyPrivate(mock).invoke("record", ArgumentMatchers.anyString());
+        assertEquals(10000, result);
+    }
+
+}