Mock a constructor with parameter

Question

I have a class as below   public class A       public A String test            bla bla bla            public String check             bla bla bla           The logic in the constructor A String test  and check   are the things I am trying to mock  I want any calls like  new A    any string     check   returns a dummy string  test    I tried    A a   mock A class     when a check    thenReturn  test      String test   a check       to this point  everything works  test shows as  tests    whenNew A class  withArguments Matchers anyString    thenReturn rk       also tried     whenNew A class  withParameterTypes String class  withArguments Matchers anyString    thenReturn rk     new A  random string   check        this doesn t work   But it doesn t seem to be working  new A    any string     check   is still going through the constructor logic instead of fetch the mocked object of A

User · Answer

With mockito you can use withSettings    for example if the CounterService required 2 dependencies  you can pass them as a mock   UserService userService   Mockito mock UserService class    SearchService searchService   Mockito mock SearchService class    CounterService counterService   Mockito mock CounterService class    withSettings   useConstructor userService  searchService

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Without Using Powermock      See the example below based on Ben Glasser answer since it took me some time to figure it out   hope that saves some times      Original Class    public class AClazz        public void updateObject CClazz cClazzObj            log debug  Bundler set             cClazzObj setBundler new BClazz cClazzObj  10               Modified Class     Slf4j public class AClazz        public void updateObject CClazz cClazzObj            log debug  Bundler set             cClazzObj setBundler getBObject cClazzObj  10               protected BClazz getBObject CClazz cClazzObj  int i            return new BClazz cClazzObj  10              Test Class   public class AClazzTest         InjectMocks      Spy     private AClazz aClazzObj        Mock     private CClazz cClazzObj        Mock     private BClazz bClassObj        Before     public void setUp   throws Exception           Mockito doReturn bClassObj                  when aClazzObj                  getBObject Mockito eq cClazzObj   Mockito anyInt                 Test     public void testConfigStrategy             aClazzObj updateObject cClazzObj            Mockito verify cClazzObj  Mockito times 1   setBundler bClassObj

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Starting with version 3 5 0 of Mockito and using the InlineMockMaker  you can now mock object constructions   try  MockedConstruction mocked   mockConstruction A class        A a   new A       when a check    thenReturn  quot bar quot        Inside the try-with-resources construct all object constructions are returning a mock

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To my knowledge  you can t mock constructors with mockito  only methods   But according to the wiki on the Mockito google code page there is a way to mock the constructor behavior by creating a method in your class which return a new instance of that class   then you can mock out that method   Below is an excerpt directly from the Mockito wiki      Pattern 1 - using one-line methods for object creation      To use pattern 1  testing a class called MyClass   you would replace a call like     Foo foo   new Foo  a  b  c          with     Foo foo   makeFoo  a  b  c          and write a one-line method     Foo makeFoo  A a  B b  C c              return new Foo  a  b  c               It s important that you don t include any logic in the method  just the one line that creates the   object  The reason for this is that the method itself is never going   to be unit tested       When you come to test the class  the object that you test will   actually be a Mockito spy  with this method overridden  to return a   mock  What you re testing is therefore not the class itself  but a   very slightly modified version of it       Your test class might contain members like     Mock private Foo mockFoo    private MyClass toTest   spy new MyClass           Lastly  inside your test method you mock out the call to   makeFoo with a line like    doReturn  mockFoo          when  toTest          makeFoo  any  A class    any  B class    any  C class           You can use matchers that are more specific than any   if you want to   check the arguments that are passed to the constructor    If you re just wanting to return a mocked object of your class I think this should work for you   In any case you can read more about mocking object creation here   http   code google com p mockito wiki MockingObjectCreation

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Mockito has limitations testing final  static  and private methods   with jMockit testing library  you can do few stuff very easy and straight-forward as below   Mock constructor of a java io File class   new MockUp lt File gt          Mock     public void  init String pathname           System out println pathname              or do whatever you want             the public constructor name should be replaced with  init     arguments and exceptions thrown remains same     return type should be defined as void   Mock a static method    remove static from the method mock signature method signature remains same otherwise

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The code you posted works for me with the latest version of Mockito and Powermockito  Maybe you haven t prepared A  Try this   A java  public class A        private final String test       public A String test            this test   test             public String check             return  checked     this test            MockA java  import static org hamcrest MatcherAssert assertThat  import static org hamcrest Matchers equalTo  import static org mockito Mockito mock  import static org mockito Mockito when   import org junit Test  import org junit runner RunWith  import org mockito Mockito  import org powermock api mockito PowerMockito  import org powermock core classloader annotations PrepareForTest  import org powermock modules junit4 PowerMockRunner    RunWith PowerMockRunner class   PrepareForTest A class  public class MockA        Test     public void test not mocked   throws Throwable           assertThat new A  random string   check    equalTo  checked random string                Test     public void test mocked   throws Throwable            A a   mock A class             when a check    thenReturn  test             PowerMockito whenNew A class  withArguments Mockito anyString    thenReturn a            assertThat new A  random string   check    equalTo  test               Both tests should pass with mockito 1 9 0  powermockito 1 4 12 and junit 4 8 2

[java] Mock a constructor with parameter

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