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/*
* Copyright (c) 2007 Mockito contributors
* This program is made available under the terms of the MIT License.
*/
package org.mockito;
import org.mockito.internal.MockitoCore;
import org.mockito.internal.creation.MockSettingsImpl;
import org.mockito.internal.stubbing.answers.*;
import org.mockito.internal.stubbing.defaultanswers.*;
import org.mockito.internal.verification.VerificationModeFactory;
import org.mockito.internal.verification.api.VerificationMode;
import org.mockito.runners.MockitoJUnitRunner;
import org.mockito.stubbing.*;
/**
*
* Mockito library enables mocks creation, verification and stubbing.
*
* This javadoc content is also available on the http://mockito.org web page.
* All documentation is kept in javadocs because it guarantees consistency between what's on the web and what's in the source code.
* Also, it makes possible to access documentation straight from the IDE even if you work offline.
*
*
* Following examples mock a List, because everyone knows its interface (methods
* like add(), get(), clear() will be used).
* You probably wouldn't mock List class 'in real'.
*
*
* Once created, mock will remember all interactions. Then you can selectively
* verify whatever interaction you are interested in.
*
*
2. How about some stubbing?
*
*
* //You can mock concrete classes, not only interfaces
* LinkedList mockedList = mock(LinkedList.class);
*
* //stubbing
* when(mockedList.get(0)).thenReturn("first");
* when(mockedList.get(1)).thenThrow(new RuntimeException());
*
* //following prints "first"
* System.out.println(mockedList.get(0));
*
* //following throws runtime exception
* System.out.println(mockedList.get(1));
*
* //following prints "null" because get(999) was not stubbed
* System.out.println(mockedList.get(999));
*
* //Although it is possible to verify a stubbed invocation, usually it's just redundant
* //If your code cares what get(0) returns then something else breaks (often before even verify() gets executed).
* //If your code doesn't care what get(0) returns then it should not be stubbed. Not convinced? See here.
* verify(mockedList).get(0);
*
*
*
*
By default, for all methods that return value, mock returns null, an
* empty collection or appropriate primitive/primitive wrapper value (e.g: 0,
* false, ... for int/Integer, boolean/Boolean, ...).
*
*
Stubbing can be overridden: for example common stubbing can go to
* fixture setup but the test methods can override it.
* Please note that overridding stubbing is a potential code smell that points out too much stubbing
*
*
Once stubbed, the method will always return stubbed value regardless
* of how many times it is called.
*
*
Last stubbing is more important - when you stubbed the same method with
* the same arguments many times.
*
*
*
*
3. Argument matchers
*
* Mockito verifies argument values in natural java style: by using an equals() method.
* Sometimes, when extra flexibility is required then you might use argument matchers:
*
*
* //stubbing using built-in anyInt() argument matcher
* when(mockedList.get(anyInt())).thenReturn("element");
*
* //stubbing using hamcrest (let's say isValid() returns your own hamcrest matcher):
* when(mockedList.contains(argThat(isValid()))).thenReturn("element");
*
* //following prints "element"
* System.out.println(mockedList.get(999));
*
* //you can also verify using an argument matcher
* verify(mockedList).get(anyInt());
*
*
*
* Argument matchers allow flexible verification or stubbing.
* {@link Matchers Click here to see} more built-in matchers
* and examples of custom argument matchers / hamcrest matchers.
*
* For information solely on custom argument matchers check out javadoc for {@link ArgumentMatcher} class.
*
* Be reasonable with using complicated argument matching.
* The natural matching style using equals() with occasional anyX() matchers tend to give clean & simple tests.
* Sometimes it's just better to refactor the code to allow equals() matching or even implement equals() method to help out with testing.
*
* Also, read section 15 or javadoc for {@link ArgumentCaptor} class.
* {@link ArgumentCaptor} is a special implementation of an argument matcher that captures argument values for further assertions.
*
* Warning on argument matchers:
*
* If you are using argument matchers, all arguments have to be provided
* by matchers.
*
* E.g: (example shows verification but the same applies to stubbing):
*
*
* verify(mock).someMethod(anyInt(), anyString(), eq("third argument"));
* //above is correct - eq() is also an argument matcher
*
* verify(mock).someMethod(anyInt(), anyString(), "third argument");
* //above is incorrect - exception will be thrown because third argument is given without an argument matcher.
*
*
*
4. Verifying exact number of invocations / at least x / never
*
*
* //using mock
* mockedList.add("once");
*
* mockedList.add("twice");
* mockedList.add("twice");
*
* mockedList.add("three times");
* mockedList.add("three times");
* mockedList.add("three times");
*
* //following two verifications work exactly the same - times(1) is used by default
* verify(mockedList).add("once");
* verify(mockedList, times(1)).add("once");
*
* //exact number of invocations verification
* verify(mockedList, times(2)).add("twice");
* verify(mockedList, times(3)).add("three times");
*
* //verification using never(). never() is an alias to times(0)
* verify(mockedList, never()).add("never happened");
*
* //verification using atLeast()/atMost()
* verify(mockedList, atLeastOnce()).add("three times");
* verify(mockedList, atLeast(2)).add("five times");
* verify(mockedList, atMost(5)).add("three times");
*
*
*
*
* times(1) is the default. Therefore using times(1) explicitly can be
* omitted.
*
*
*
* Read more about doThrow|doAnswer family of methods in paragraph 12.
*
* Initially, {@link Mockito#stubVoid(Object)} was used for stubbing voids.
* Currently stubVoid() is deprecated in favor of {@link Mockito#doThrow(Throwable)}.
* This is because of improved readability and consistency with the family of {@link Mockito#doAnswer(Answer)} methods.
*
*
6. Verification in order
*
*
* List firstMock = mock(List.class);
* List secondMock = mock(List.class);
*
* //using mocks
* firstMock.add("was called first");
* secondMock.add("was called second");
*
* //create inOrder object passing any mocks that need to be verified in order
* InOrder inOrder = inOrder(firstMock, secondMock);
*
* //following will make sure that firstMock was called before secondMock
* inOrder.verify(firstMock).add("was called first");
* inOrder.verify(secondMock).add("was called second");
*
*
* Verification in order is flexible - you don't have to verify all
* interactions one-by-one but only those that you are interested in
* testing in order.
*
* Also, you can create InOrder object passing only mocks that are relevant for
* in-order verification.
*
*
7. Making sure interaction(s) never happened on mock
*
*
* //using mocks - only mockOne is interacted
* mockOne.add("one");
*
* //ordinary verification
* verify(mockOne).add("one");
*
* //verify that method was never called on a mock
* verify(mockOne, never()).add("two");
*
* //verify that other mocks were not interacted
* verifyZeroInteractions(mockTwo, mockThree);
*
*
*
* A word of warning:
* Some users who did a lot of classic, expect-run-verify mocking tend to use verifyNoMoreInteractions() very often, even in every test method.
* verifyNoMoreInteractions() is not recommended to use in every test method.
* verifyNoMoreInteractions() is a handy assertion from the interaction testing toolkit. Use it only when it's relevant.
* Abusing it leads to overspecified, less maintainable tests. You can find further reading
* here.
*
*
* See also {@link Mockito#never()} - it is more explicit and
* communicates the intent well.
*
*
*
9. Shorthand for mocks creation - @Mock annotation
*
*
*
Minimizes repetitive mock creation code.
*
Makes the test class more readable.
*
Makes the verification error easier to read because the field name
* is used to identify the mock.
*
* Sometimes we need to stub with different return value/exception for the same
* method call. Typical use case could be mocking iterators.
* Original version of Mockito did not have this feature to promote simple mocking.
* For example, instead of iterators one could use {@link Iterable} or simply
* collections. Those offer natural ways of stubbing (e.g. using real
* collections). In rare scenarios stubbing consecutive calls could be useful,
* though:
*
*
* Allows stubbing with generic {@link Answer} interface.
*
* Yet another controversial feature which was not included in Mockito
* originally. We recommend using simple stubbing with thenReturn() or
* thenThrow() only. Those two should be just enough to test/test-drive
* any clean & simple code.
*
*
12. doThrow()|doAnswer()|doNothing()|doReturn() family of methods for stubbing voids (mostly)
*
* Stubbing voids requires different approach from {@link Mockito#when(Object)} because the compiler does not like void methods inside brackets...
*
* {@link Mockito#doThrow(Throwable)} replaces the {@link Mockito#stubVoid(Object)} method for stubbing voids.
* The main reason is improved readability and consistency with the family of doAnswer() methods.
*
* Use doThrow() when you want to stub a void method with an exception:
*
*
* You can create spies of real objects. When you use the spy then the real methods are called (unless a method was stubbed).
*
* Real spies should be used carefully and occasionally, for example when dealing with legacy code.
*
*
* Spying on real objects can be associated with "partial mocking" concept.
* Before the release 1.8, Mockito spies were not real partial mocks.
* The reason was we thought partial mock is a code smell.
* At some point we found legitimate use cases for partial mocks
* (3rd party interfaces, interim refactoring of legacy code, the full article is here)
*
*
*
* List list = new LinkedList();
* List spy = spy(list);
*
* //optionally, you can stub out some methods:
* when(spy.size()).thenReturn(100);
*
* //using the spy calls real methods
* spy.add("one");
* spy.add("two");
*
* //prints "one" - the first element of a list
* System.out.println(spy.get(0));
*
* //size() method was stubbed - 100 is printed
* System.out.println(spy.size());
*
* //optionally, you can verify
* verify(spy).add("one");
* verify(spy).add("two");
*
*
*
Important gotcha on spying real objects!
*
* 1. Sometimes it's impossible to use {@link Mockito#when(Object)} for stubbing spies. Example:
*
*
* List list = new LinkedList();
* List spy = spy(list);
*
* //Impossible: real method is called so spy.get(0) throws IndexOutOfBoundsException (the list is yet empty)
* when(spy.get(0)).thenReturn("foo");
*
* //You have to use doReturn() for stubbing
* doReturn("foo").when(spy).get(0);
*
*
* 2. Watch out for final methods.
* Mockito doesn't mock final methods so the bottom line is: when you spy on real objects + you try to stub a final method = trouble.
* What will happen is the real method will be called *on mock* but *not on the real instance* you passed to the spy() method.
* Typically you may get a NullPointerException because mock instances don't have fields initiated.
*
*
14. Changing default return values of unstubbed invocations (Since 1.7)
*
* You can create a mock with specified strategy for its return values.
* It's quite advanced feature and typically you don't need it to write decent tests.
* However, it can be helpful for working with legacy systems.
*
* It is the default answer so it will be used only when you don't stub the method call.
*
*
* Read more about this interesting implementation of Answer: {@link Mockito#RETURNS_SMART_NULLS}
*
*
15. Capturing arguments for further assertions (Since 1.8.0)
*
* Mockito verifies argument values in natural java style: by using an equals() method.
* This is also the recommended way of matching arguments because it makes tests clean & simple.
* In some situations though, it is helpful to assert on certain arguments after the actual verification.
* For example:
*
*
* Warning: it is recommended to use ArgumentCaptor with verification but not with stubbing.
* Using ArgumentCaptor with stubbing may decrease test readability because captor is created outside of assert (aka verify or 'then') block.
* Also it may reduce defect localization because if stubbed method was not called then no argument is captured.
*
* In a way ArgumentCaptor is related to custom argument matchers (see javadoc for {@link ArgumentMatcher} class).
* Both techniques can be used for making sure certain arguments where passed to mocks.
* However, ArgumentCaptor may be a better fit if:
*
*
custom argument matcher is not likely to be reused
*
you just need it to assert on argument values to complete verification
*
* Custom argument matchers via {@link ArgumentMatcher} are usually better for stubbing.
*
*
16. Real partial mocks (Since 1.8.0)
*
* Finally, after many internal debates & discussions on the mailing list, partial mock support was added to Mockito.
* Previously we considered partial mocks as code smells. However, we found a legitimate use case for partial mocks - more reading:
* here
*
* Before release 1.8 spy() was not producing real partial mocks and it was confusing for some users.
* Read more about spying: here or in javadoc for {@link Mockito#spy(Object)} method.
*
*
* //you can create partial mock with spy() method:
* List list = spy(new LinkedList());
*
* //you can enable partial mock capabilities selectively on mocks:
* Foo mock = mock(Foo.class);
* //Be sure the real implementation is 'safe'.
* //If real implementation throws exceptions or depends on specific state of the object then you're in trouble.
* when(mock.someMethod()).thenCallRealMethod();
*
*
* As usual you are going to read the partial mock warning:
* Object oriented programming is more less tackling complexity by dividing the complexity into separate, specific, SRPy objects.
* How does partial mock fit into this paradigm? Well, it just doesn't...
* Partial mock usually means that the complexity has been moved to a different method on the same object.
* In most cases, this is not the way you want to design your application.
*
* However, there are rare cases when partial mocks come handy:
* dealing with code you cannot change easily (3rd party interfaces, interim refactoring of legacy code etc.)
* However, I wouldn't use partial mocks for new, test-driven & well-designed code.
*
*
17. Resetting mocks (Since 1.8.0)
*
* Smart Mockito users hardly use this feature because they know it could be a sign of poor tests.
* Normally, you don't need to reset your mocks, just create new mocks for each test method.
*
* Instead of reset() please consider writing simple, small and focused test methods over lengthy, over-specified tests.
* First potential code smell is reset() in the middle of the test method. This probably means you're testing too much.
* Follow the whisper of your test methods: "Please keep us small & focused on single behavior".
* There are several threads about it on mockito mailing list.
*
* The only reason we added reset() method is to
* make it possible to work with container-injected mocks.
* See issue 55 (here)
* or FAQ (here).
*
* Don't harm yourself. reset() in the middle of the test method is a code smell (you're probably testing too much).
*
* List mock = mock(List.class);
* when(mock.size()).thenReturn(10);
* mock.add(1);
*
* reset(mock);
* //at this point the mock forgot any interactions & stubbing
*
* Next, you should know that Mockito validates if you use it correctly all the time.
* However, there's a gotcha so please read the javadoc for {@link Mockito#validateMockitoUsage()}
*
*
19. Aliases for behavior driven development (Since 1.8.0)
*
* Behavior Driven Development style of writing tests uses //given //when //then comments as fundamental parts of your test methods.
* This is exactly how we write our tests and we warmly encourage you to do so!
*
* The problem is that current stubbing api with canonical role of when word does not integrate nicely with //given //when //then comments.
* It's because stubbing belongs to given component of the test and not to the when component of the test.
* Hence {@link BDDMockito} class introduces an alias so that you stub method calls with {@link BDDMockito#given(Object)} method.
* Now it really nicely integrates with the given component of a BDD style test!
*
*
* Mocks can be made serializable. With this feature you can use a mock in a place that requires dependencies to be serializable.
*
* WARNING: This should be rarely used in unit testing.
*
* The behaviour was implemented for a specific use case of a BDD spec that had an unreliable external dependency. This
* was in a web environment and the objects from the external dependency were being serialized to pass between layers.
*
* To create serializable mock use {@link MockSettings#serializable()}:
*
* List serializableMock = mock(List.class, withSettings().serializable());
*
* Making a real object spy serializable is a bit more effort as the spy(...) method does not have an overloaded version
* which accepts MockSettings. No worries, you will hardly ever use it.
*
*
* List
*/
@SuppressWarnings("unchecked")
public class Mockito extends Matchers {
private static final MockitoCore MOCKITO_CORE = new MockitoCore();
/**
* The default Answer of every mock if the mock was not stubbed.
* Typically it just returns some empty value.
*
* {@link Answer} can be used to define the return values of unstubbed invocations.
*
* This implementation first tries the global configuration.
* If there is no global configuration then it uses {@link ReturnsEmptyValues} (returns zeros, empty collections, nulls, etc.)
*/
public static final Answer
