sebastianbergmann/phpunit · error · InvalidDataProviderException

Data Provider method %s::%s() expects an argument

Error message

Data Provider method %s::%s() expects an argument

What it means

Thrown while resolving a data provider when the method declares at least one parameter (ReflectionMethod::getNumberOfParameters() > 0). PHPUnit invokes providers with zero arguments, so a provider that expects parameters cannot be called and is rejected.

Source

Thrown at src/Metadata/Api/DataProvider.php:149

                            'Data Provider method %s::%s() is not public',
                            $className,
                            $methodName,
                        ),
                    );
                }

                if (!$method->isStatic()) {
                    throw new InvalidDataProviderException(
                        sprintf(
                            'Data Provider method %s::%s() is not static',
                            $className,
                            $methodName,
                        ),
                    );
                }

                if ($method->getNumberOfParameters() > 0) {
                    throw new InvalidDataProviderException(
                        sprintf(
                            'Data Provider method %s::%s() expects an argument',
                            $className,
                            $methodName,
                        ),
                    );
                }

                /** @phpstan-ignore staticMethod.dynamicName */
                $data = $className::$methodName();

                if (!is_iterable($data)) {
                    throw new InvalidDataProviderException(
                        sprintf(
                            'Data Provider method %s::%s() does not return an iterable',
                            $className,
                            $methodName,
                        ),

View on GitHub (pinned to f123cdb2a2)

Solutions

1. Remove the parameters from the provider method and resolve any needed values inside its body
2. If configuration is needed, read it from constants/env/fixures within the provider instead of parameters

Example fix

// before
public static function provideCases(int $count): array
{
    return array_fill(0, $count, [1]);
}

// after
public static function provideCases(): array
{
    $count = 3;

    return array_fill(0, $count, [1]);
}

$method = new ReflectionMethod($testClass, 'provideCases');

if ($method->getNumberOfParameters() > 0) {
    // refactor to a zero-parameter provider before running
}

function isValidDataProvider(ReflectionMethod $method): bool
{
    return $method->isPublic()
        && $method->isStatic()
        && $method->getNumberOfParameters() === 0;
}

When it happens

Trigger: A provider method with a signature like 'public static function provideCases(string $context): array' referenced through @dataProvider.

Common situations: Providers that were originally helper methods taking arguments; refactorings that injected configuration parameters into a previously parameterless provider.

Related errors

• Data Provider method %s::%s() is not public
• Data Provider method %s::%s() is not static
• Comparison method %s::%s() does not exist.
• Comparison method %s::%s() does not declare exactly one para
• Return value for %s::%s() cannot be generated: %s

AI-assisted analysis of sebastianbergmann/phpunit@f123cdb2a2 (2026-08-23). Data as JSON: /api/errors/1ffaa792367b44b2. Report an issue: GitHub.