4.x: MockBean fails with ArgumentMatcher

[romain-grecourt]

Environment Details

• Helidon Version: 4.0.12
• Helidon MP

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Problem Description

If a test uses an argument matcher, it fails with the following error:

org.mockito.exceptions.misusing.InvalidUseOfMatchersException: 
Misplaced or misused argument matcher detected here:

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When mocked instances are created in ApplicationScoped the injected instance is a client proxy, and the mocked instance is lazily created on first usage. This breaks when using argument matchers.

A work-around is to call toString() on the mocked instance to force the creation of the mock before using matchers on the mocked instance.

Steps to reproduce

@MockBean
private Service service;

@Test
void testArgumentMatcher() {
    Mockito.when(service.test(anyString())).thenReturn("Mocked");
}