quarkusio/quarkus · error · IllegalArgumentException

className parameter is required

Error message

className parameter is required

What it means

Dev UI's one-shot testing feature registers a JSON-RPC action to run a single test class (optionally a method). The handler requires the 'className' request parameter; when it is absent or blank, registerRunTestMethod throws IllegalArgumentException. This is a client-input validation error for the run-test endpoint.

Source

Thrown at extensions/devui/deployment/src/main/java/io/quarkus/devui/deployment/menu/OneShotTestingProcessor.java:149

                .build();
    }

    private void registerRunTestMethod(LaunchModeBuildItem launchModeBuildItem, BuildTimeActionBuildItem actions) {
        actions.actionBuilder()
                .methodName(RUN_TEST_NAME)
                .description(RUN_TEST_DESC)
                .parameter("className", "The fully qualified test class name, e.g. com.example.MyTest")
                .parameter("methodName",
                        "The test method name to run. If not provided, all tests in the class are run.",
                        false)
                .function(params -> {
                    Optional<TestSupport> ts = TestSupport.instance();
                    if (testsDisabled(launchModeBuildItem, ts)) {
                        return CompletableFuture.completedFuture(null);
                    }
                    String className = params.get("className");
                    if (className == null || className.isBlank()) {
                        throw new IllegalArgumentException("className parameter is required");
                    }
                    String methodName = params.get("methodName");
                    String testSelection = className;
                    if (methodName != null && !methodName.isBlank()) {
                        testSelection = className + "#" + methodName;
                    }
                    final String selection = testSelection;
                    return CompletableFuture.supplyAsync(() -> {
                        compileTestSources();
                        TestRunResults results = ts.get().runSpecificTestSynchronously(selection);
                        return results != null ? new TrimmedTestRunResult(results) : null;
                    }, executor).orTimeout(TEST_TIMEOUT_MINUTES, TimeUnit.MINUTES);
                })
                .enableMcpFunctionByDefault()
                .build();
    }

    private void registerCancelTestsMethod(LaunchModeBuildItem launchModeBuildItem, BuildTimeActionBuildItem actions) {

View on GitHub (pinned to e1c734241f)

Solutions

1. Pass a fully-qualified test class name in the 'className' parameter, e.g. com.example.MyTest.
2. Optionally include 'methodName' to target a single method; className remains mandatory.
3. Check the calling code/UI for parameter naming ('className', not 'class' or 'testClass').
4. Trim the value — whitespace-only strings are rejected the same as null.

Example fix

// before
Map<String, String> params = Map.of("methodName", "testFoo");

// after
Map<String, String> params = Map.of("className", "com.example.MyTest", "methodName", "testFoo");

String className = params.get("className");
if (className == null || className.isBlank()) {
    throw new IllegalArgumentException("Provide a fully-qualified test class name in 'className'");
}

try { runOneShotTest(params); }
catch (IllegalArgumentException e) {
    if (e.getMessage().equals("className parameter is required")) {
        ui.showError("Select a test class before running");
    } else throw e;
}

When it happens

Trigger: Calling the Dev UI one-shot testing 'run test' action with params lacking 'className', or with className set to null/empty/whitespace — e.g. invoking the action programmatically or from a customized UI without selecting a test.

Common situations: Scripted JSON-RPC calls to the Dev UI endpoint missing the parameter; custom Dev UI extensions or scripts calling the action; tests-disabled early-return not hit because TestSupport exists, then the blank parameter slips through.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

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AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/d8f7f09dcaca6025. Report an issue: GitHub.