testcontainers/testcontainers-java · warning

can't be reused because it overrides

Error message

{} can't be reused because it overrides {}

What it means

GenericContainer.canBeReused() checks that the container subclass does not override containerIsCreated(String); overriding hooks would not run when reusing an existing container, breaking behavior. If an override is found it logs a warning ('{} can't be reused because it overrides {}') and returns false, so reuse (withReuse(true)) is disabled for that class.

Solutions

1. Remove the containerIsCreated override and move setup logic into an earlier lifecycle hook (e.g. configure())
2. Accept the warning — reuse is intentionally disabled for this subclass
3. Subclass differently: apply custom setup before container creation rather than after

Example fix

// before
@Override
protected void containerIsCreated(String containerId) { setup(); }
// after
@Override
protected void configure() { /* setup expressed as config */ }

// detect reuse-incompatible subclasses early
for (Class<?> t = custom.getClass(); t != GenericContainer.class; t = t.getSuperclass()) {
    try { t.getDeclaredMethod("containerIsCreated", String.class);
          throw new IllegalStateException(t + " overrides containerIsCreated; reuse disabled"); }
    catch (NoSuchMethodException ignored) {}
}

When it happens

Trigger: Using .withReuse(true) on a container subclass that overrides containerIsCreated; the container silently falls back to creating a fresh instance per run.

Common situations: Custom container classes overriding containerIsCreated for extra setup; upgrading testcontainers while keeping legacy lifecycle overrides; confusion about why container reuse is not taking effect despite identical hashes.

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

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AI-assisted analysis of testcontainers/testcontainers-java@8e549514e3 (2026-09-12). Data as JSON: /api/errors/dc8eef820d00ea5d. Report an issue: GitHub.

Appendix: source

Thrown at core/src/main/java/org/testcontainers/containers/GenericContainer.java:357

                            startupAttempts
                        );
                    tryStart();
                    return true;
                }
            );
        } catch (Exception e) {
            throw new ContainerLaunchException("Container startup failed for image " + getDockerImageName(), e);
        }
    }

    @UnstableAPI
    @SneakyThrows
    protected boolean canBeReused() {
        for (Class<?> type = getClass(); type != GenericContainer.class; type = type.getSuperclass()) {
            try {
                Method method = type.getDeclaredMethod("containerIsCreated", String.class);
                if (method.getDeclaringClass() != GenericContainer.class) {
                    logger().warn("{} can't be reused because it overrides {}", getClass(), method.getName());
                    return false;
                }
            } catch (NoSuchMethodException | NoClassDefFoundError e) {
                // ignore
            }
        }

        return true;
    }

    private void tryStart() {
        try {
            String dockerImageName = getDockerImageName();
            logger().debug("Starting container: {}", dockerImageName);

            Instant startedAt = Instant.now();
            logger().info("Creating container for image: {}", dockerImageName);
            CreateContainerCmd createCommand = dockerClient.createContainerCmd(dockerImageName);

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