apache/beam · error · UnsupportedOperationException

.hashCode() is not supported.

Error message

%s.hashCode() is not supported.

What it means

PAssert's PCollectionContentsAssert (IterableAssert) intentionally breaks Object.hashCode: calling hashCode() always throws UnsupportedOperationException. Combined with the broken equals(), this prevents PAssert objects from being used in hash-based collections, which would be meaningless for an assertion object.

Solutions

1. Don't store PAssert assertion objects in hash-based collections; run each assertion directly
2. Keep references in a List and iterate to invoke the assertion methods
3. If identity grouping is needed, wrap in your own holder class with a valid hashCode/equals

Example fix

// before
Set<IterableAssert<?>> asserts = new HashSet<>();
asserts.add(assertThat(pcollection));
// after
List<IterableAssert<?>> asserts = new ArrayList<>();
asserts.add(assertThat(pcollection));

if (obj instanceof org.apache.beam.sdk.testing.PAssert.IterableAssert) {
  throw new IllegalStateException("PAssert objects cannot be hashed or used as map keys");
}

boolean isHashable(Object o) {
  return !(o instanceof org.apache.beam.sdk.testing.PAssert.IterableAssert);
}

try {
  Set<Object> set = new HashSet<>(assertObjects);
} catch (UnsupportedOperationException e) {
  if (e.getMessage().contains("hashCode() is not supported")) {
    // switch to a List or wrap in a holder with valid hashCode
  }
}

When it happens

Trigger: Using a PAssert assertion object as a HashMap key, in a HashSet, with Collectors.toMap/groupingBy, or any hashing utility (e.g. Objects.hash(assertObj), Guava Hashing) on the assert object.

Common situations: Collecting multiple PAssert objects into a Set for batch evaluation; passing assert objects into hashing-based test utilities; accidentally logging with a framework that hashes objects.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• If you meant to test object equality, use…
• List of SerializableFunction must be the same size as the…
• List of SerializableFunction must not be null
• tests for Java equality of the
• assert_that must be used within a beam.Pipeline context…

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/0bd65b7ecc731b1d. Report an issue: GitHub.

Appendix: source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/testing/PAssert.java:814

     * @deprecated {@link Object#equals(Object)} is not supported on PAssert objects. If you meant
     *     to test object equality, use a variant of {@link #containsInAnyOrder} instead.
     */
    @Deprecated
    @Override
    @SuppressFBWarnings("EQ_UNUSUAL")
    public boolean equals(@Nullable Object o) {
      throw new UnsupportedOperationException(
          "If you meant to test object equality, use .containsInAnyOrder instead.");
    }

    /**
     * @throws UnsupportedOperationException always.
     * @deprecated {@link Object#hashCode()} is not supported on PAssert objects.
     */
    @Deprecated
    @Override
    public int hashCode() {
      throw new UnsupportedOperationException(
          String.format("%s.hashCode() is not supported.", IterableAssert.class.getSimpleName()));
    }
  }

  /**
   * An {@link IterableAssert} for an iterable that is the sole element of a {@link PCollection}.
   * This does not require the runner to support side inputs.
   */
  private static class PCollectionSingletonIterableAssert<T> implements IterableAssert<T> {
    private final PCollection<Iterable<T>> actual;
    private final Coder<T> elementCoder;
    private final AssertionWindows rewindowingStrategy;
    private final SimpleFunction<Iterable<ValueInSingleWindow<Iterable<T>>>, Iterable<Iterable<T>>>
        paneExtractor;
    private final PAssertionSite site;

    public PCollectionSingletonIterableAssert(
        PCollection<Iterable<T>> actual, PAssertionSite site) {

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