@CustomTestApplication value cannot be annotated with @HiltAndroidApp

I have an application that needs injection:

@HiltAndroidApp
class MyApplication: Application() {
    @Inject lateinit var printerFactory: PrinterFactory
    ...
}

Other code in the app uses application.printerFactory.

The printerFactory is provided by this:

@Module
@InstallIn(ApplicationComponent::class)
object ProdModule {
    @Provides
    fun providePrinterFactory(): PrinterFactory {
        return FactoryThatReturnsARealPrinter()
    }
}

Now, for instrumented tests, I need to override this with a test version:

@HiltAndroidTest
@UninstallModules(ProdModule::class)
@RunWith(AndroidJUnit4::class)
@LargeTest
class MainTest {
    @get:Rule(order = 0)
    var hiltRule = HiltAndroidRule(this)

    @get:Rule(order = 1)
    var intentsTestRule = IntentsTestRule(MainActivity::class.java, false, false)

    // Test replacements for production stuff.
    @Module
    @InstallIn(ApplicationComponent::class)
    class TestModule {
        @Provides
        fun providePrinterFactory(): PrinterFactory {
            return FactoryThatReturnsATestPrinter()
        }
    }
    ...
}

And so I get this error:

java.lang.IllegalStateException: Hilt test, MainTest, cannot use a @HiltAndroidApp application but found MyApplication. To fix, configure the test to use HiltTestApplication or a custom Hilt test application generated with @CustomTestApplication.

Well, I can’t use HiltTestApplication because I need to use MyApplication, which has dependencies injected.

So I added this:

    @CustomTestApplication(MyApplication::class)
    interface HiltTestApplication

And so I get this error:

error: [Hilt]
    public static abstract interface HiltTestApplication {
                           ^
  @CustomTestApplication value cannot be annotated with @HiltAndroidApp. Found: MyApplication

If MyApplication cannot be annotated with @HiltAndroidApp, then how is it expected to inject things?

Instructions unclear, ended up in inconsistent state.