android test support flavors and build type variants?
    flavorDimensions "foo"
    productFlavors {
        full {
            dimension "foo"
        }
        trial {
            dimension "foo"
        }
    }
If there is only src/androidTest/java, which variant to test?
You can create tests for specific flavors in src/androidTestFull and src/androidTestTrial. Any tests that are common to all flavors go in src/androidTest.
The instrumented tests in src/androidTest/ source set are shared by all build variants. When building a test APK for the "MyFlavor" variant of your app, Gradle combines both the src/androidTest/ and src/androidTestMyFlavor/ source sets.
来源:https://stackoverflow.com/questions/48895869/android-test-support-flavors-and-build-type-variants