title: Junit cannot Mock a class
body: <p>I'm having problem when I try to test a method and mock its dependency with PowerMock and Mockito. I've tried to transform the dependency method into a nonstatic method and to use @Mock annotation and @InjectMocks but with no result at all.</p>
  
  <p>Here is the class and method under test:</p>
  
  <pre><code>/* class to be tested */
  public class LoginServiceImpl implements LoginService{
  
     /* method to be tested */
     @Override
     public String createJwt(String subject, String name, String permission, Date datenow)  throws java.io.UnsupportedEncodingException{
         Date expDate = datenow;
         expDate.setTime(datenow.getTime()+(300*1000));  //expiration time = 30 minutes
  
         String token = jwtUtils.generateJwt(subject, expDate, name, permission);
         return token;
     }
  }
  </code></pre>
  
  <p>Here there is the Dependency I want to Mock and which I am having troubles mocking:</p>
  
  <pre><code>/* Dependency I cannot mock */
  public class JwtUtils {
  
      public static String generateJwt(String subject, Date date, String name, String scope) throws java.io.UnsupportedEncodingException{
          String jwt = Jwts.builder()
              .setSubject(subject)
              .setExpiration(date)
              .claim("name", name)
              .claim("scope", scope)
              .signWith(
                      SignatureAlgorithm.HS256,
                      "myPersonalSecretKey12345".getBytes("UTF-8")
              )
              .compact();
  
         return jwt;
     }
  }
  </code></pre>
  
  <p>And here at last, but not least, the test class with the test method which fails.
  I have to say that it doesn't even reach the assert method call, but fails at when().thenResult().
  I have also to specify that I've tried to use doReturn() and any() as matcher, but with not result.</p>
  
  <pre><code>@RunWith(MockitoJUnitRunner.class)          //to run Mockito
  @PrepareForTest({JwtUtils.class})           //powerMock annotations tomock classes containing static methods
  public class LoginServiceImplTest {
  
     @InjectMocks
     LoginServiceImpl loginService;          //System under test (SUT)
  
     @Test
     public void createJwtTest() throws Exception {
  
         SimpleDateFormat ft = new SimpleDateFormat("yyyy-MM-dd");
         Date expdate = ft.parse("2040-12-12");
         String jwt = JwtUtils.generateJwt("BDAGPP32E08F205K", expdate, "Pippo Baudo", "conduttore");
         //HERE IT'S WHERE IT FAILS:
         when(JwtUtils.generateJwt("BDAGPP32E08F205K", expdate, "Pippo Baudo", "conduttore")).thenReturn(jwt);
  
         assertThat(loginService.createJwt("BDAGPP32E08F205K", "Pippo Baudo", "conduttore", expdate), is(jwt));
     }
  }
  </code></pre>
  
  <p>Here there is the error JUnit and Mockito gives to me:</p>
  
  <blockquote>
    <p>org.mockito.exceptions.misusing.MissingMethodInvocationException:  when() requires an argument which has to be 'a method call on a mock'.
    For example:
        when(mock.getArticles()).thenReturn(articles);</p>
    
    <p>Also, this error might show up because:
    1. you stub either of: final/private/equals()/hashCode() methods.    Those methods <em>cannot</em> be stubbed/verified.    Mocking methods
    declared on non-public parent classes is not supported.
    2. inside when() you don't call method on mock but on some other object.</p>
    
    <p>at
    com.example.bytecode.SpringBootJWT.services.LoginServiceImplTest.createJwtTest1(LoginServiceImplTest.java:114)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)  at
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
      at
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.lang.reflect.Method.invoke(Method.java:498)     at
    org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
      at
    org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
      at
    org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
      at
    org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
      at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)    at
    org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
      at
    org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
      at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)  at
    org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)   at
    org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)     at
    org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)   at
    org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)  at
    org.junit.runners.ParentRunner.run(ParentRunner.java:363)     at
    org.mockito.internal.runners.JUnit45AndHigherRunnerImpl.run(JUnit45AndHigherRunnerImpl.java:37)
      at
    org.mockito.runners.MockitoJUnitRunner.run(MockitoJUnitRunner.java:62)
      at org.junit.runner.JUnitCore.run(JUnitCore.java:137)   at
    com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
      at
    com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
      at
    com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
      at
    com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)</p>
    
    <p>Process finished with exit code 255</p>
  </blockquote>