Constructor parameter resolution for outer class fails while using @Nested and test template context provider

[A248]

@Nested, constructor parameter resolution, and test template context providers don't play well together.

This is best demonstrated by example:

@ExtendWith(ContextProvider.class)
public class FailingTest {

    private final Token token;

    public FailingTest(Token token) { // Supplied by test template context provider
        this.token = token;
    }

    @TestTemplate
    public void runOuter() {
       // Passes
    }

    @Nested
    @ExtendWith(ContextProvider.class)
    public class Inner {

        @TestTemplate
        public void runInner() {
          // FAILS!
        }
    }
}

Description

Test templates can provide additional extensions according to the TestTemplateInvocationContextProvider and the invocation context it supplies.

Those extensions can include parameter resolvers. Normally, this works fine.

However, when using @Nested, the constructor parameters on the outer class cannot be resolved by the extension.

Steps to reproduce

Reproducer here:
https://github.com/A248/junit-ctor-params-nested-context-provider-reproducer

Context

• Used versions (Jupiter/Vintage/Platform): 5.14.3

[marcphilipp]

This is a general limitation of @Nested test classes:

junit-framework/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/NestedClassTestDescriptor.java

Line 106 in a6e2a8b

// Extensions registered for nested classes and below are not to be used for instantiating and initializing outer classes

So, it wouldn't work even if you had registered ContextProvider.ProvideParameterExtension on the @Nested test class.

Have you considered putting the parameter on the @TestTemplate methods or using a @ClassTemplate instead?

[A248]

Is there anything at all that can be used to instantiate the outer class?

Based on what you're telling me, it would seem that outer classes are severely limited and can't accept any parameters whatsoever, no matter how I configure things.

[marcphilipp]

Outer classes can accept parameters, it's just that ParameterResolver extensions need to be registered outside of nested classes.

Please provide more details about your use case. I'm sure we can find a solution.

[A248]

Well for my use case, I use @TestTemplate to set-up complicated integration tests and provide relevant context. It's the TestTemplateInvocationContextProvider that supplies resources related to these tests: databases, managers, controllers, etc. A lot of my integration test infrastructure is built around it.

Hiterto I've operated under the assumption that the above setup with @TestTemplate can control all aspects of the test. After all, the context provider can supply all kinds of extensions, and I use these for generic pre-test and post-test setup that is shared across the test infrastructure. Parameter resolution is just one feature among many that I control through @TestTemplate.

This is why I was somewhat surprised to encounter this issue; I had often used constructor parameters across my test codebase, and I was accustomed to them "just working" thanks to the invocation context provider. However, this is the first time I'm finding something that the context provider cannot do, it seems.

I'm not sure how I would get the invocation context provider to supply the ParameterResolver for the outer class constructor parameters. This is the limitation that led me to open this issue.

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