[Testing] Mockito fails with ArrayStoreException on JDK 8 due to JSpecify TYPE_USE annotations

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Needs clarification
Activity status
Quiet
Tech stack
java
Domain
testing-qa

Research direction

Start by running the Maven testing phase on JDK 8 with a generated Stub or Client class using JSpecify annotations and a standard Mockito mock. Compare the failing declaration-based mock with Mockito.mock(..., Mockito.withSettings().withoutAnnotations()). The issue names no target file or acceptance criteria, so the intended fix and definition of done need clarification.

Written by the indexing model from the issue text.

Description

priority: p3 type: bug

Description
Mockito tests running on Java 8 (JDK 1.8) crash with an ArrayStoreException / EnumConstantNotPresentExceptionProxy when attempting to mock generated Stub or Client classes that contain JSpecify annotations (@NullMarked or @Nullable).

Because JSpecify uses Type-Use (TYPE_USE) annotations, it triggers a known limitation in standard JDK 8 Java Reflection API. Standard JVM annotation parsers throw an ArrayStoreException when bytecode scanners (like ByteBuddy, underneath Mockito) introspect parameterized types, arrays, or generic descriptors holding Type-Use annotations.

Workaround
Handwritten tests aiming to maintain backwards compatibility with Java 8 while using JSpecify must explicitly disable annotation processing on mocked generated classes. Instead of standard @Mock Declaration annotations, instantiations must use:
Mockito.mock(MyStub.class, Mockito.withSettings().withoutAnnotations());.

This workaround has been successfully applied in the following integration PRs:

#13702
#13612
#13621

Reproducer
Steps to reproduce:

  1. Generate GAPIC veneers/stubs annotated with JSpecify @NullMarked or @Nullable (Type-Use).
  2. Write a handwritten unit test using Java 8 runtime.
  3. Instantiate standard Mockito mock for the generated class: MetricServiceStub mockStub = Mockito.mock(MetricServiceStub.class); or @Mock private MetricServiceStub mockStub;.
  4. Run tests and observe ArrayStoreException crash.

Code Snippets:

Failing Snippet (Standard/Declaration):

@Mock private MetricServiceStub mockMetricServiceStub; // Crashes on JDK 8
Bypass/Working Snippet (Programmatic without annotations):

private MetricServiceStub mockMetricServiceStub;

@Before
public void setUp() {
// Bypasses reflection parser crash
mockMetricServiceStub = Mockito.mock(
MetricServiceStub.class,
Mockito.withSettings().withoutAnnotations()
);
}

Logs and Stack Trace

org.mockito.exceptions.base.MockitoException:
Mockito cannot mock this class: class com.google.cloud.monitoring.v3.stub.MetricServiceStub.

Mockito can only mock non-private & non-final classes, but the root cause of this error might be different.
...
Caused by: java.lang.ArrayStoreException: sun.reflect.annotation.EnumConstantNotPresentExceptionProxy
at java.lang.Class.createAnnotationData(Class.java:3521)
at java.lang.Class.annotationData(Class.java:3510)
at java.lang.Class.getDeclaredAnnotations(Class.java:3477)

Behavior
When did the issue begin? Began following PR integrations introducing JSpecify Type-Use annotations (@NullMarked, @Nullable) to generated surfaces.
Is this behavior flaky? No, it is consistently seen during the Maven Testing Phase running specifically on JDK 1.8.

Dominant language
Java
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Merged PRs (30d)
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