Overloaded method issues with strict

When adding mocks for overloaded methods using Strict, Mockito throws an error that the wrong method was mocked.

mockito 2.22.0, JDK 1.8.0_181

package test;

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.junit.jupiter.MockitoExtension;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.mockito.ArgumentMatchers.any;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.when;

@ExtendWith(MockitoExtension.class)
class MockitoTest {

    @Test
    void validateStrictness() {
        MyInterface myInterface = mock(MyInterface.class);
        String expected1 = "oneArgument";
        String expected2 = "twoArguments";
        when(myInterface.getString(any())).thenReturn(expected1);
        when(myInterface.getString(any(), any())).thenReturn(expected2);

        String actual = myInterface.getString("one");
        assertEquals(actual, expected1);
        actual = myInterface.getString("one", "two");
        assertEquals(actual, expected2);
    }

    public interface MyInterface {
        String getString(String one);

        String getString(String one, String two);
    }
}

org.mockito.exceptions.misusing.PotentialStubbingProblem: 
Strict stubbing argument mismatch. Please check:
 - this invocation of 'getString' method:
    myInterface.getString(null, null);
    -> at test.MockitoTest.validateStrictness(MockitoTest.java:21)
 - has following stubbing(s) with different arguments:
    1. myInterface.getString(null);
      -> at test.MockitoTest.validateStrictness(MockitoTest.java:20)
Typically, stubbing argument mismatch indicates user mistake when writing tests.
Mockito fails early so that you can debug potential problem easily.
However, there are legit scenarios when this exception generates false negative signal:
  - stubbing the same method multiple times using 'given().will()' or 'when().then()' API
    Please use 'will().given()' or 'doReturn().when()' API for stubbing.
  - stubbed method is intentionally invoked with different arguments by code under test
    Please use default or 'silent' JUnit Rule (equivalent of Strictness.LENIENT).
For more information see javadoc for PotentialStubbingProblem class.

    at test.MockitoTest.validateStrictness(MockitoTest.java:21)


Process finished with exit code 255

[DavidTanner]

It looks like this has to do with calling when the second time. I couldn’t find what was going on, but the second when doesn’t attempt to add the mock logic, it just calls the method. Replacing with doReturn().when() works.

        doReturn(expected1).when(overloadedMethods).getString(any());
        doReturn(expected2).when(overloadedMethods).getString(any(), any());

[DavidTanner]

Looking at the code, the issue appears to be from a naive stub comparison. The parameters of the method aren’t compared, just the name.

https://github.com/mockito/mockito/blob/v2.22.0/src/main/java/org/mockito/internal/junit/DefaultStubbingLookupListener.java#L59-L60