added code snippets for bael-4554 (#9979)

testing-modules/mockito-2/src/main/java/com/baeldung/mockito/whenvsdomethods/Employee.java

@@ -0,0 +1,11 @@
+package com.baeldung.mockito.whenvsdomethods;
+
+import java.time.DayOfWeek;
+
+public interface Employee {
+
+    String greet();
+    
+    void work(DayOfWeek day);
+    
+}

testing-modules/mockito-2/src/main/java/com/baeldung/mockito/whenvsdomethods/IAmOnHolidayException.java

@@ -0,0 +1,5 @@
+package com.baeldung.mockito.whenvsdomethods;
+
+public class IAmOnHolidayException extends RuntimeException {
+
+}

testing-modules/mockito-2/src/test/java/com/baeldung/mockito/whenvsdomethods/WhenVsDoMethodsUnitTest.java

@@ -0,0 +1,90 @@
+package com.baeldung.mockito.whenvsdomethods;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertThat;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.mockito.BDDMockito.given;
+import static org.mockito.BDDMockito.willThrow;
+import static org.mockito.Mockito.doReturn;
+import static org.mockito.Mockito.doThrow;
+import static org.mockito.Mockito.when;
+
+import java.time.DayOfWeek;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.function.Executable;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+
+public class WhenVsDoMethodsUnitTest {
+
+    @Mock
+    private Employee employee;
+
+    @BeforeEach
+    void setup() {
+        MockitoAnnotations.initMocks(this);
+    }
+
+    @Test
+    void givenNonVoidMethod_callingWhen_shouldConfigureBehavior() {
+        // given
+        when(employee.greet()).thenReturn("Hello");
+
+        // when
+        String greeting = employee.greet();
+
+        // then
+        assertThat(greeting, is("Hello"));
+    }
+
+    @Test
+    void givenNonVoidMethod_callingDoReturn_shouldConfigureBehavior() {
+        // given
+        doReturn("Hello").when(employee).greet();
+
+        // when
+        String greeting = employee.greet();
+
+        // then
+        assertThat(greeting, is("Hello"));
+    }
+
+    @Test
+    void givenVoidMethod_callingDoThrow_shouldConfigureBehavior() {
+        // given
+        doThrow(new IAmOnHolidayException()).when(employee).work(DayOfWeek.SUNDAY);
+
+        // when
+        Executable workCall = () -> employee.work(DayOfWeek.SUNDAY);
+
+        // then
+        assertThrows(IAmOnHolidayException.class, workCall);
+    }
+
+    @Test
+    void givenNonVoidMethod_callingGiven_shouldConfigureBehavior() {
+        // given
+        given(employee.greet()).willReturn("Hello");
+
+        // when
+        String greeting = employee.greet();
+
+        // then
+        assertThat(greeting, is("Hello"));
+    }
+
+    @Test
+    void givenVoidMethod_callingWillThrow_shouldConfigureBehavior() {
+        // given
+        willThrow(new IAmOnHolidayException()).given(employee).work(DayOfWeek.SUNDAY);
+
+        // when
+        Executable workCall = () -> employee.work(DayOfWeek.SUNDAY);
+
+        // then
+        assertThrows(IAmOnHolidayException.class, workCall);
+    }
+
+}