Play tests with mocked Lagom services fails to build Injector

Since Lagom 1.5.0 there’s a new ServiceClientModule Guice module that service clients will get loaded by default. The ServiceClientModule was introduced in https://github.com/lagom/lagom/pull/1385/files#diff-32 and indirectly requires a ServiceLocator.

Play users that inject a Lagom Service.Descriptor on their code usually mock that on their tests. The problem with the appearance of ServiceClientModule is that Play tests with mocked Lagom instances now get ServiceClientModule unnecessarily. On top of that, the tests will probably fail because they lack a ServiceLocator required by ServiceClientModule but completely unnecessary for a Play unit test.

The symptoms are a Guice error:

[error] 1) No implementation for com.lightbend.lagom.javadsl.api.ServiceLocator was bound.
[error]   while locating com.lightbend.lagom.javadsl.api.ServiceLocator
[error]     for the 4th parameter of com.lightbend.lagom.internal.javadsl.client.JavadslServiceClientImplementor.<init>(JavadslServiceClientImplementor.scala:46)
[error]   at com.lightbend.lagom.internal.javadsl.client.ServiceClientModule.bindings(ServiceClientModule.scala:15):
[error] Binding(class com.lightbend.lagom.internal.javadsl.client.JavadslServiceClientImplementor to self) (via modules: com.google.inject.util.Modules$OverrideModule -> play.api.inject.guice.GuiceableModuleConversions$$anon$4)
[error] 
[error] 1 error, took 0.148 sec
[error]     at com.google.inject.internal.Errors.throwCreationExceptionIfErrorsExist(Errors.java:543)
[error]     at com.google.inject.internal.InternalInjectorCreator.initializeStatically(InternalInjectorCreator.java:159)
[error]     at com.google.inject.internal.InternalInjectorCreator.build(InternalInjectorCreator.java:106)
[error]     at com.google.inject.Guice.createInjector(Guice.java:87)
[error]     at com.google.inject.Guice.createInjector(Guice.java:78)
[error]     at play.api.inject.guice.GuiceBuilder.injector(GuiceInjectorBuilder.scala:201)
[error]     at play.inject.guice.GuiceBuilder.injector(GuiceBuilder.java:211)
[error]     at play.inject.guice.GuiceApplicationBuilder.build(GuiceApplicationBuilder.java:121)

And a workaround is to disable the ServiceClientModule from the Injector since the Lagom clients are being mocked:

// In MyFrontendControllerTest.java

  @Before
  public void setup() {
     // mock Lagom services
     mockCustomersService = mock(CustomersService.class);
     mockOrderService = mock(OrderService.class);

     application = new GuiceApplicationBuilder()
      .overrides(bind(OrderService.class).toInstance(mockOrderService))
      .overrides(bind(CustomersService.class).toInstance(mockCustomersService))
      .disable(ServiceClientModule.class) // Add this line.
      .build();

    server = Helpers.testServer(application);
    server.start();
 }

[ignasi35]

What about reverting back to just-in-time bindings? My concern is that this workaround is really not going to be obvious to most users.

SGTM, the efforts driving into a non-Guice specific implementation to be more CDI compatible seem stalled.

[TimMoore]

I debugged this a bit more, and understand what’s happening now. Guice isn’t eagerly instantiating the binding, but it does validate that explicit bindings are injectable when creating the injector. This makes some sense: you generally don’t want things to fail at runtime deep within some request because the DI system hasn’t been wired up properly.

I think the only options would be to:

1. Provide a test helper for Play apps that use Lagom clients that binds TestServiceLocator, just like the Lagom ServiceTest does.
2. Revert back to just-in-time (implicit) bindings for JavadslServiceClientImplementor and ServiceClientLoader.