NullPointerException thrown by instrumented metrics code in unit tests.

[slavaschmidt]

Version used: 2.2.1

There seem to be an issue with using @FlushMetrics annotation that leads to the NullPointerException during automated testing.

Our project is managed with maven.

This is how out test is implemented:

    @Test
    void Can_handle_request() {
        final APIGatewayProxyRequestEvent apiGatewayProxyRequestEvent = mock(APIGatewayProxyRequestEvent.class);
        final Context context = mock(Context.class);
        given(context.getAwsRequestId()).willReturn("request-id");

        final APIGatewayProxyResponseEvent actual = requestHandler.handleRequest(apiGatewayProxyRequestEvent, context);
        // assertions

    }

and the implementation:

    @Override
    @FlushMetrics(namespace = "namespace", service = "service", captureColdStart = true)
    public APIGatewayProxyResponseEvent handleRequest(
        final APIGatewayProxyRequestEvent apiGatewayProxyRequestEvent,
        final Context context
    ) {
// actual implementation
}

We pass environment variables to disable metrics as in the following (pom.xml):

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-surefire-plugin</artifactId>
    <configuration>
        <environmentVariables>
            <POWERTOOLS_SERVICE_NAME>test</POWERTOOLS_SERVICE_NAME>
            <POWERTOOLS_METRICS_DISABLED>true</POWERTOOLS_METRICS_DISABLED>
            <POWERTOOLS_METRICS_NAMESPACE>test</POWERTOOLS_METRICS_NAMESPACE>
            <POWERTOOLS_METRICS_FUNCTION_NAME>test</POWERTOOLS_METRICS_FUNCTION_NAME>
            <POWERTOOLS_DISABLE_METRICS>true</POWERTOOLS_DISABLE_METRICS>
        </environmentVariables>
    </configuration>
</plugin>

Still, when tests are executed a NullPointerException is thrown by the instrumented code.

java.lang.NullPointerException
        at java.base/java.util.concurrent.ConcurrentHashMap.putVal(ConcurrentHashMap.java:1011)
        at java.base/java.util.concurrent.ConcurrentHashMap.put(ConcurrentHashMap.java:1006)
        at software.amazon.cloudwatchlogs.emf.model.Metadata.putCustomMetadata(Metadata.java:89)
        at software.amazon.cloudwatchlogs.emf.model.MetricsContext.putMetadata(MetricsContext.java:273)
        at software.amazon.cloudwatchlogs.emf.logger.MetricsLogger.lambda$putMetadata$5(MetricsLogger.java:277)
        at software.amazon.cloudwatchlogs.emf.logger.MetricsLogger.applyReadLock(MetricsLogger.java:328)
        at software.amazon.cloudwatchlogs.emf.logger.MetricsLogger.putMetadata(MetricsLogger.java:275)
        at software.amazon.lambda.powertools.metrics.internal.EmfMetricsLogger.addMetadata(EmfMetricsLogger.java:94)
        at software.amazon.lambda.powertools.metrics.internal.LambdaMetricsAspect.captureColdStartMetricIfEnabled(LambdaMetricsAspect.java:116)
        at software.amazon.lambda.powertools.metrics.internal.LambdaMetricsAspect.around(LambdaMetricsAspect.java:97)
        at com.acme.RequestHandler.handleRequest(RequestHandler.java:67)
        at com.acme.RequestHandlerTest.Can_handle_request(RequestHandlerTest.java:116)
        at java.base/java.lang.reflect.Method.invoke(Method.java:580)
        at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
        at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)

[phipag]

Hey @slavaschmidt, thanks for reporting this. Let me try to reproduce your issue.

[phipag]

I just tried to reproduce your example but I don't see the NullPointerException in my environment. Can you share some more details about your project? Your Java version, junit version, mockito version, maven surefire version?

I am using this code setup:

public class EmfFunction implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {
    private static final Metrics metrics = MetricsFactory.getMetricsInstance();

    @Override
    @FlushMetrics(namespace = "namespace", service = "service", captureColdStart = true)
    public APIGatewayProxyResponseEvent handleRequest(final APIGatewayProxyRequestEvent input, final Context context) {
        emitDummyMetrics();

        final APIGatewayProxyResponseEvent response = new APIGatewayProxyResponseEvent();
        return response
                .withStatusCode(200)
                .withBody("Emitted dummy metrics using EMF");
    }

    private void emitDummyMetrics() {
        for (int i = 0; i < 500; i++) {
            String metricName = "DummyCountMetric";
            metrics.addMetric(metricName, 1, MetricUnit.COUNT);
        }
    }
}

class EmfFunctionTest {

    private final EmfFunction requestHandler = new EmfFunction();

    @Test
    void Can_handle_request() {
        final APIGatewayProxyRequestEvent apiGatewayProxyRequestEvent = mock(APIGatewayProxyRequestEvent.class);
        final Context context = mock(Context.class);
        given(context.getAwsRequestId()).willReturn("request-id");

        final APIGatewayProxyResponseEvent actual = requestHandler.handleRequest(apiGatewayProxyRequestEvent, context);

        assertEquals(200, actual.getStatusCode());
        assertEquals("Emitted dummy metrics using EMF", actual.getBody());
    }
}

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>3.5.3</version>
                <configuration>
                    <environmentVariables>
                        <POWERTOOLS_SERVICE_NAME>test</POWERTOOLS_SERVICE_NAME>
                        <POWERTOOLS_METRICS_DISABLED>true</POWERTOOLS_METRICS_DISABLED>
                        <POWERTOOLS_METRICS_NAMESPACE>test</POWERTOOLS_METRICS_NAMESPACE>
                        <POWERTOOLS_METRICS_FUNCTION_NAME>test</POWERTOOLS_METRICS_FUNCTION_NAME>
                        <POWERTOOLS_DISABLE_METRICS>true</POWERTOOLS_DISABLE_METRICS>
                    </environmentVariables>
                </configuration>
            </plugin>

[INFO] -------------------------------------------------------
[INFO]  T E S T S
[INFO] -------------------------------------------------------
[INFO] Running org.demo.emfputmetricbenchmark.EmfFunctionTest
OpenJDK 64-Bit Server VM warning: Sharing is only supported for boot loader classes because bootstrap classpath has been appended
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.742 s -- in org.demo.emfputmetricbenchmark.EmfFunctionTest
[INFO] 
[INFO] Results:
[INFO] 
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

[phipag]

Side note: The POWERTOOLS_DISABLE_METRICS can be removed. This is a mistake in our documentation. The correct variable name is POWERTOOLS_METRICS_DISABLED. I will fix this part in our docs.

[phipag]

Hey @slavaschmidt,

I reproduced your issue in a triaging project and found the problem. The problem is with mocking the Lambda Context object.

This NullPointerException is raised because the mocked context returns null for getAwsRequestId(). To fix this, you can either mock this method to return a string value or alternatively implement a TestContext like I am doing here:

• Sample unit test: https://github.com/phipag/powertools-triaging-template-java/blob/72dbbb717f62e42f23ce3a1e886fc8eb5966258a/src/test/java/triage/TriageHandlerTest.java#L15-L31
• Sample TestContext: https://github.com/phipag/powertools-triaging-template-java/blob/72dbbb717f62e42f23ce3a1e886fc8eb5966258a/src/test/java/triage/TestContext.java