How to use shouldKnowIfIsSerializable method of org.mockito.internal.creation.DelegatingMethodTest class

It is quite easy with Mockito:

@RunWith(MockitoJUnitRunner.class)
public class RuleIdValidatorTest {
    @Mock
    private RuleStore ruleStoreMock;

    @InjectMocks
    private RuleIdValidator ruleIdValidator;

    @Test
    public void someTest() {
        when(ruleStoreMock.doSomething("arg")).thenReturn("result");

        String actual = ruleIdValidator.doSomeThatDelegatesToRuleStore();

        assertEquals("result", actual);
    }
}

Read more about @InjectMocks in the Mockito javadoc or in a blog post that I wrote about the topic some time ago.

Available as of Mockito 1.8.3, enhanced in 1.9.0.

What you are asking is not possible because your legacy code relies on a static method getInstance() and Mockito does not allow to mock static methods, so the following line won't work

when(FormatterService.getInstance()).thenReturn(formatter);

There are 2 ways around this problem:

1. Use a different mocking tool, such as PowerMock, that allows to mock static methods.

2. Refactor your code, so that you don't rely on the static method. The least invasive way I can think of to achieve this is by adding a constructor to DriverSnapshotHandler that injects a FormatterService dependency. This constructor will be only used in tests and you production code will continue to use the real singleton instance.

   public static class DriverSnapshotHandler {
   
       private final FormatterService formatter;
   
       //used in production code
       public DriverSnapshotHandler() {
           this(FormatterService.getInstance());
       }
   
       //used for tests
       DriverSnapshotHandler(FormatterService formatter) {
           this.formatter = formatter;
       }
   
       public String getImageURL() {
           return formatter.formatTachoIcon();
       }
   }
   

Then, your test should look like this :

FormatterService formatter = mock(FormatterService.class);
when(formatter.formatTachoIcon()).thenReturn("MockedURL");
DriverSnapshotHandler handler = new DriverSnapshotHandler(formatter);
handler.getImageURL();
verify(formatter, atLeastOnce()).formatTachoIcon();

Since you are loading configuration class MyApplication.class datasource bean will be created, Try moving datasource in another bean which is not used in a test, make sure all classes loaded for tests are not dependant on datasource.
Or
In your tests create a config class marked with @TestConfiguration and include it in SpringBootTest(classes=TestConfig.class) mocking data source there like

@Bean
public DataSource dataSource() {
    return Mockito.mock(DataSource.class);
}

But this may fail since method call to this mocked datasouce for connection will return null, In that case, you'll have to create an in-memory datasource and then mock jdbcTemplate and rest of dependencies.

The easiest (only?) approach, IMHO, would be to use the thenAnswer method, which allows you to not only return a value, but actually execute some code. Java 8 makes this particularly elegant, as you could just use an anonymous lambda:

when(myMock.myFunction(anyString()))
    .thenAnswer(i -> new MyObject((String)i.getArguments()[0]);

Use this :

import static org.mockito.Mockito.verifyZeroInteractions;

// ...

private PrintStream backup = System.out;

@Before
public void setUp() {
    System.setOut(mock(PrintStream.class));
}

@After
public void tearDown() {
    verifyZeroInteractions(System.out);
    System.setOut(backup);
}

You should use thenReturn or doReturn when you know the return value at the time you mock a method call. This defined value is returned when you invoke the mocked method.

thenReturn(T value) Sets a return value to be returned when the method is called.

@Test
public void test_return() throws Exception {
    Dummy dummy = mock(Dummy.class);
    int returnValue = 5;

    // choose your preferred way
    when(dummy.stringLength("dummy")).thenReturn(returnValue);
    doReturn(returnValue).when(dummy).stringLength("dummy");
}

Answer is used when you need to do additional actions when a mocked method is invoked, e.g. when you need to compute the return value based on the parameters of this method call.

Use doAnswer() when you want to stub a void method with generic Answer.

Answer specifies an action that is executed and a return value that is returned when you interact with the mock.

@Test
public void test_answer() throws Exception {
    Dummy dummy = mock(Dummy.class);
    Answer<Integer> answer = new Answer<Integer>() {
        public Integer answer(InvocationOnMock invocation) throws Throwable {
            String string = invocation.getArgumentAt(0, String.class);
            return string.length() * 2;
        }
    };

    // choose your preferred way
    when(dummy.stringLength("dummy")).thenAnswer(answer);
    doAnswer(answer).when(dummy).stringLength("dummy");
}

You need a Method object and a Class object. As per your comment, Mockito cannot mock a Method, so you'll need a real one. I haven't tested this, but I believe this would work. Instead of:

when(mockContext.getMethod().getName()).thenReturn("someMethod");
when(mockContext.getMethod().getDeclaringClass().getName()).thenReturn("someClass");

You need:

// any method will do, but here is an example of how to get one.
Method testMethod = this.getClass().getMethod("logCallTest");

when(mockContext.getMethod()).thenReturn(testMethod);

Obviously, getName() will not return "someMethod" anymore and getDeclaringClass().getName() will return the name of this test class (in the example), but although you couldn't pick what they return, what they return is still deterministic, so you should be able to verify anything you need. (Of course, if you needed to spy or verify that a call was made on the Method object itself, you're still stuck.)

proguard-maven-plugin will obfuscate the primary artifact of your project, not the secondary artifact jar-with-dependencies that the maven-assembly-plugin generated.

You need to configure the plugin to obfuscate the jar-with-dependencies by specifying the injar attribute:

Specifies the input jar name (or wars, ears, zips) of the application to be processed.

<injar>${project.build.finalName}-jar-with-dependencies.jar</injar>

Now, there is also a problem in the order of execution of plugins in your POM: we need to make sure that the maven-assembly-plugin is executed before the proguard-maven-plugin. As such, it is best to define an explicit execution for the maven-assembly-plugin bound to the package phase instead of manually invoking it from the command line with assembly:single. This would be the configuration:

<plugin>
    <artifactId>maven-assembly-plugin</artifactId>
    <executions>
        <execution>
            <id>assembly</id>
            <goals>
                <goal>single</goal>
            </goals>
            <phase>package</phase>
            <configuration>
                <descriptorRefs>
                    <descriptorRef>jar-with-dependencies</descriptorRef>
                </descriptorRefs>
            </configuration>
        </execution>
    </executions>
</plugin>

and then, you just need to make sure that the proguard-maven-plugin plugin configuration is after that in your POM.

Having done that, invoking Maven with mvn clean install will result in an obfuscated jar with dependencies.

To test with your actual POM, I added two repositories:

• https://repo.spongepowered.org/maven to resolve the spongeapi dependency.
• http://maven.restlet.com to resolve the org.restlet.jse dependencies.

With those 2 dependencies, warnings were generated by ProGuard because the org.restlet.ext.jackson dependency utilizes com.sun.msv.* classes that are not on the buildpath. Since I figure that your code is currently working, it means those classes don't need to be included and that those warnings can be ignored. As such, I added the -dontwarn option so that ProGuard doesn't error when there is a warning.

The final POM for which I was able to successfully obfuscate the jar with dependencies is the following:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.mycompany</groupId>
    <artifactId>myproduct</artifactId>
    <version>1.0-SNAPSHOT</version>
    <repositories>
       <repository>
           <id>spongepowered</id>
           <url>https://repo.spongepowered.org/maven</url>
       </repository>
       <repository>
           <id>restlet</id>
           <url>http://maven.restlet.com</url>
       </repository>
    </repositories>
    <properties>
        <restlet-version>2.3.5</restlet-version>
    </properties>
    <build>
       <resources>
            <resource>
                <directory>${project.basedir}/src/main/resources</directory>
                <filtering>true</filtering>
            </resource>
        </resources>
        <plugins>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.3</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>templating-maven-plugin</artifactId>
                <version>1.0-alpha-3</version>
                <executions>
                    <execution>
                        <id>filter-src</id>
                        <goals>
                            <goal>filter-sources</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <artifactId>maven-assembly-plugin</artifactId>
                <executions>
                    <execution>
                        <id>assembly</id>
                        <goals>
                            <goal>single</goal>
                        </goals>
                        <phase>package</phase>
                        <configuration>
                            <descriptorRefs>
                                <descriptorRef>jar-with-dependencies</descriptorRef>
                            </descriptorRefs>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>com.github.wvengen</groupId>
                <artifactId>proguard-maven-plugin</artifactId>
                <version>2.0.8</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals><goal>proguard</goal></goals>
                        <configuration>
                            <injar>${project.build.finalName}-jar-with-dependencies.jar</injar> <!-- make sure to obfuscate the jar with dependencies -->
                            <proguardVersion>5.2</proguardVersion>
                            <options>
                                <option>-allowaccessmodification</option>
                                <option>-dontoptimize</option>
                                <option>-dontshrink</option>
                                <option>-dontnote</option>
                                <option>-dontwarn</option> <!-- added option to ignore com.sun missing classes -->
                                <option>-keepattributes Signature</option>
                                <option>-keep class com.mycompany.MyPlugin { *; }</option>
                            </options>
                            <libs>
                                <lib>${java.home}/lib/rt.jar</lib>
                            </libs>
                            <dependencies>
                                <dependency>
                                    <groupId>net.sf.proguard</groupId>
                                    <artifactId>proguard-base</artifactId>
                                    <version>5.2</version>
                                    <scope>runtime</scope>
                                </dependency>
                            </dependencies>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
    <dependencies>
       <dependency>
            <groupId>org.spongepowered</groupId>
            <artifactId>spongeapi</artifactId>
            <version>3.0.0</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
        <dependency>
            <groupId>org.easytesting</groupId>
            <artifactId>fest-assert-core</artifactId>
            <version>2.0M8</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.mockito</groupId>
            <artifactId>mockito-core</artifactId>
            <version>1.10.19</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.restlet.jse</groupId>
            <artifactId>org.restlet</artifactId>
            <version>${restlet-version}</version>
        </dependency>
        <dependency>
            <groupId>org.restlet.jse</groupId>
            <artifactId>org.restlet.ext.jackson</artifactId>
            <version>${restlet-version}</version>
        </dependency>
        <dependency>
            <groupId>com.googlecode.json-simple</groupId>
            <artifactId>json-simple</artifactId>
            <version>1.1.1</version>
        </dependency>
    </dependencies>
</project>

Using void reset(T... mocks) will reset all stubbings on the mocks. If you just need to reset the invocation counts for subsequent verifications, use void clearInvocations(T... mocks).