JUnit+Mockito无法Mock方法调用，报InvalidUseOfMatchersException错误求助

Hey there! Let's break down why you're hitting that InvalidUseOfMatchersException when mocking your isOwner method—this is a super common pitfall for folks new to Mockito, so we’ll get it sorted out.

Common Causes for This Exception #

Let’s walk through the most likely reasons you’re seeing this error:

• Mixing matchers and raw values: Mockito doesn’t allow combining argument matchers (like anyArgs(), anyString()) with real concrete values in the same method call. For example, when(xxx.isOwner("realUserId", anyLong())).thenReturn(true) will throw the error because the first parameter is a raw string while the second is a matcher.
• Incorrect doReturn syntax: If you wrote something like doReturn(someData).when(xxx.isOwner(anyArgs())), that’s wrong. The when() call should only take your mock object, not the method invocation. The method call with matchers comes after the when() block.
• Missing static imports for matchers: If you’re using anyArgs() but haven’t imported Mockito’s static matcher methods, Mockito won’t recognize it as a valid matcher, leading to the exception.
• Mocking a real instance: If the xxx object you’re trying to mock is a real, instantiated service (not created via @Mock or Mockito.mock()), calling mock methods on it will fail.

Fixes to Try #

Let’s go step by step to fix this:

1. Align your argument usage:
   If you use any matchers, wrap all arguments in matchers. Use eq() to turn raw values into matchers when you need to target specific inputs. For example:

   // Correct: All arguments use matchers
   when(xxx.isOwner(eq("specificUserId"), anyLong())).thenReturn(true);
   

2. Fix your doReturn syntax:
   The correct structure for doReturn is:

   // Right way: Pass mock to when(), then call the method with matchers
   doReturn(true).when(xxx).isOwner(anyArgs());
   

   Avoid putting the method call inside the when() parentheses—that triggers a real method call and breaks matcher logic.
3. Add static imports:
   Make sure you’ve imported Mockito’s static methods to use matchers properly. Add this at the top of your test class:

   import static org.mockito.Mockito.*;
   

4. Verify your mock is a real Mock instance:
   Ensure your xxx object is created as a mock, not a real service. Use either:
   • The @Mock annotation (with @ExtendWith(MockitoExtension.class) for JUnit 5, or @RunWith(MockitoJUnitRunner.class) for JUnit 4), or
   • Manual mock creation: YourService xxx = Mockito.mock(YourService.class);

Example of Correct Mocking #

Suppose your isOwner method has the signature boolean isOwner(String userId, Long resourceId)—here’s how to mock it properly with both styles:

Using when(...).thenReturn()

when(xxx.isOwner(anyString(), anyLong())).thenReturn(true);
// Or for specific values
when(xxx.isOwner(eq("testUser123"), eq(456L))).thenReturn(true);

Using doReturn(...).when()

doReturn(true).when(xxx).isOwner(anyString(), anyLong());
// Or for specific values
doReturn(true).when(xxx).isOwner(eq("testUser123"), eq(456L));

Start by checking these points—chances are one of them is the root of your issue!

内容的提问来源于stack exchange，提问作者Bhagyesh