Configuring JUnit4 on Android — The Right Runner, Registry, and Matrix

Almost every "test suite is misconfigured" report boils down to one of three root causes: the wrong AndroidJUnit4 is imported, the wrong InstrumentationRegistry is imported, or the size-annotation / dispatcher plumbing is missing. This skill encodes the exact Gradle matrix from androidx.test:core 1.7.0 onward, the canonical FQCNs, and the minimal MainDispatcherRule pattern that androidx itself ships in testutils-ktx.

When to use this skill

• The user reports Cannot resolve symbol AndroidJUnit4, AndroidJUnit4 is deprecated, or asks "which AndroidJUnit4 should I import".
• The user reports IllegalStateException: No instrumentation registered from InstrumentationRegistry.getInstrumentation() in a unit test, or asks why InstrumentationRegistry is crossed out.
• The user wants Truth subjects (IntentSubject, BundleSubject, LocationSubject, ParcelableSubject) but does not know which artifact ships them.
• The user wants am instrument -e size small to filter tests and asks how to wire @SmallTest / @MediumTest / @LargeTest.
• The user is writing a ViewModel / coroutine test and needs the canonical MainDispatcherRule template.

When NOT to use this skill