Is there a way to have a stubbed method return different objects on subsequent invocations? I'd like to do this to test nondeterminate responses from an ExecutorCompletionService
. i.e. to test that irrespective of the return order of the methods, the outcome remains constant.
The code I'm looking to test looks something like this.
// Create an completion service so we can group these tasks together
ExecutorCompletionService<T> completionService =
new ExecutorCompletionService<T>(service);
// Add all these tasks to the completion service
for (Callable<T> t : ts)
completionService.submit(request);
// As an when each call finished, add it to the response set.
for (int i = 0; i < calls.size(); i ++) {
try {
T t = completionService.take().get();
// do some stuff that I want to test
} catch (...) { }
}
How about
when( method-call ).thenReturn( value1, value2, value3 );
You can put as many arguments as you like in the brackets of thenReturn, provided they're all the correct type. The first value will be returned the first time the method is called, then the second answer, and so on. The last value will be returned repeatedly once all the other values are used up.
You can do that using the thenAnswer
method (when chaining with when
):
when(someMock.someMethod()).thenAnswer(new Answer() {
private int count = 0;
public Object answer(InvocationOnMock invocation) {
if (count++ == 1)
return 1;
return 2;
}
});
Or using the equivalent, static doAnswer
method:
doAnswer(new Answer() {
private int count = 0;
public Object answer(InvocationOnMock invocation) {
if (count++ == 1)
return 1;
return 2;
}
}).when(someMock).someMethod();
doAnswer()
/thenAnswer()
do not allow chaining multiple calls as doReturn()
/thenReturn()
do and I needed to compute something and not just return a different value. Creating an anonymous Answer
object with a private count
variable was what did the trick for me.
someMethod()
returns void
. See this answer for more details.
As previously pointed out almost all of the calls are chainable.
So you could call
when(mock.method()).thenReturn(foo).thenReturn(bar).thenThrow(new Exception("test"));
//OR if you're mocking a void method and/or using spy instead of mock
doReturn(foo).doReturn(bar).doThrow(new Exception("Test").when(mock).method();
More info in Mockito's Documenation.
mock.method
was called in this example? I want something like, return foo the first time but return bar for ALL the rest.
Almost all of the calls are chainable:
doReturn(null).doReturn(anotherInstance).when(mock).method();
BDD style:
import static org.mockito.BDDMockito.given;
...
given(yourMock.yourMethod()).willReturn(1, 2, 3);
Classic style:
import static org.mockito.Mockito.when;
...
when(yourMock.yourMethod()).thenReturn(1, 2, 3);
Explicit style:
...
when(yourMock.yourMethod())
.thenReturn(1)
.thenReturn(2)
.thenReturn(3);
Depending on an arg
Suppose we have 2 args, and check the size of the 2nd (list) arg:
...
when(yourMock.yourMethod(any(), anyList()))
.thenAnswer(args -> ((List) args.getArgument(1)).size() < 2
? 1
: 3);
args are Objects, so we have to cast an arg to our type. I cast ^^^ to (List)
in my case.
BDD
...
given(yourMock.yourMethod(any(), anyList()))
.willAnswer(args -> ((List) args.getArgument(1)).size() < 2
? 1
: 3);
I've implemented a MultipleAnswer
class that helps me to stub different answers in every call. Here the piece of code:
private final class MultipleAnswer<T> implements Answer<T> {
private final ArrayList<Answer<T>> mAnswers;
MultipleAnswer(Answer<T>... answer) {
mAnswers = new ArrayList<>();
mAnswers.addAll(Arrays.asList(answer));
}
@Override
public T answer(InvocationOnMock invocation) throws Throwable {
return mAnswers.remove(0).answer(invocation);
}
}
doReturn( value1, value2, value3 ).when( method-call )
doReturn(value1, value2, value3).when(mock).methodCall()
perhaps?
Related to @[Igor Nikolaev]'s answer from 8 years ago, using an Answer
can be simplified somewhat using a lambda expression available in Java 8.
when(someMock.someMethod()).thenAnswer(invocation -> {
doStuff();
return;
});
or more simply:
when(someMock.someMethod()).thenAnswer(invocation -> doStuff());
If you have a dynamic list of values you can use AdditionalAnswers.returnsElementsOf
:
import org.mockito.AdditionalAnswers;
when(mock.method()).thenAnswer(AdditionalAnswers.returnsElementsOf(myListOfValues));
Following can be used as a common method to return different arguments on different method calls. Only thing we need to do is we need to pass an array with order in which objects should be retrieved in each call.
@SafeVarargs
public static <Mock> Answer<Mock> getAnswerForSubsequentCalls(final Mock... mockArr) {
return new Answer<Mock>() {
private int count=0, size=mockArr.length;
public Mock answer(InvocationOnMock invocation) throws throwable {
Mock mock = null;
for(; count<size && mock==null; count++){
mock = mockArr[count];
}
return mock;
}
}
}
Ex. getAnswerForSubsequentCalls(mock1, mock3, mock2);
will return mock1 object on first call, mock3 object on second call and mock2 object on third call. Should be used like when(something()).doAnswer(getAnswerForSubsequentCalls(mock1, mock3, mock2));
This is almost similar to when(something()).thenReturn(mock1, mock3, mock2);
This is not directly related to the question. But wanted to put this in the same chain.
If trying to verify the same method call with multiple arguments, you can use the below times feature by Mockito. You don't need it if you are not verifying.
Mockito.verify(method, times(n)).methoscall();
Here is 'n' is the number of times the mock is invoked.
This might be basic/obvious, but if like me you are trying to mock multiple calls for a method that is called unknown number of times per call to method to be tested, for example:
public String method(String testArg) {
//...
while(condition) {
someValue = someBean.nestedMethod(); // This is called unknown number of times
//...
}
//...
}
You can do something like:
@Test
public void testMethod() {
mockNestedMethodForValue("value1");
assertEquals(method("arg"), "expected1");
mockNestedMethodForValue("value2");
assertEquals(method("arg"), "expected2");
mockNestedMethodForValue("value3");
assertEquals(method("arg"), "expected3");
}
private void mockNestedMethodForValue(String value) {
doReturn(value).when(someBeanMock).nestedMethod();
}
Here is working example in BDD style which is pretty simple and clear
given(carRepository.findByName(any(String.class))).willReturn(Optional.empty()).willReturn(Optional.of(MockData.createCarEntity()));
You can use a LinkedList
and an Answer
. Eg
MyService mock = mock(MyService.class);
LinkedList<String> results = new LinkedList<>(List.of("A", "B", "C"));
when(mock.doSomething(any())).thenAnswer(invocation -> results.removeFirst());
Success story sharing
doAnswer
or to write anAnswer
in the case that you mention. You can just usedoReturn(...).when(someSpy).someMethod(...)
. It seems reasonable to assume that Emma is interested in mocks, rather than spies, but I guess I could add something to my answer to spell this out. Thanks for the comment.