Mock Lambda Context and Logger while testing AWS Lambda RequestHandler (with JUnit4)

JavaLambdaLocalTestAsJavaApplication.java.md

package com.test;

import java.io.File; import java.io.FileNotFoundException; import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; import java.util.Scanner;

import com.amazonaws.services.lambda.runtime.ClientContext; import com.amazonaws.services.lambda.runtime.Context; import com.amazonaws.services.lambda.runtime.LambdaLogger;

import software.amazon.awssdk.regions.Region; import software.amazon.awssdk.services.ssm.SsmClient;

/** */ public class JavaLambdaLocalTestAsJavaApplication {

public static void main(String[] args) throws FileNotFoundException {
	MyLambdaFunction function = new MyLambdaFunction();
	String putMsgBody = new Scanner(new File("src/test/resources/MyTestEvent.json")).useDelimiter("\\Z")
			.next();
	Context mockedContext = getContext();
	function.handleRequest(putMsgBody, mockedContext);
}

private static Context getContext() {
	Context context = new Context() {

		@Override
		public int getRemainingTimeInMillis() {
			// TODO Auto-generated method stub
			return 0;
		}

		@Override
		public int getMemoryLimitInMB() {
			// TODO Auto-generated method stub
			return 0;
		}

		@Override
		public LambdaLogger getLogger() {
			// TODO Auto-generated method stub
			return new LambdaLogger() {

				@Override
				public void log(byte[] message) {
					System.out.println(message);

				}

				@Override
				public void log(String message) {
					System.out.println(message);

				}
			};
		}

		@Override
		public String getLogStreamName() {
			// TODO Auto-generated method stub
			return null;
		}

		@Override
		public String getLogGroupName() {
			// TODO Auto-generated method stub
			return null;
		}

		@Override
		public String getInvokedFunctionArn() {
			// TODO Auto-generated method stub
			return null;
		}

		@Override
		public CognitoIdentity getIdentity() {
			// TODO Auto-generated method stub
			return null;
		}

		@Override
		public String getFunctionVersion() {
			// TODO Auto-generated method stub
			return null;
		}

		@Override
		public String getFunctionName() {
			// TODO Auto-generated method stub
			return "local-order-management";
		}

		@Override
		public ClientContext getClientContext() {
			// TODO Auto-generated method stub
			return null;
		}

		@Override
		public String getAwsRequestId() {
			// TODO Auto-generated method stub
			return "123456";
		}
	};
	return context;
}

}

LambdaRequestHandlerWithLoggerTest.java.md

//In the test class import com.amazonaws.services.lambda.runtime.Context; import com.amazonaws.services.lambda.runtime.LambdaLogger; import org.junit.runner.RunWith; import org.mockito.junit.MockitoJUnitRunner; import org.mockito.Mock; import org.junit.Before; import org.junit.Test; import static org.mockito.Mockito.when; import static org.mockito.Mockito.doAnswer; import static org.mockito.ArgumentMatchers.anyString;

@RunWith(MockitoJUnitRunner.class)//without this runner - mocks would be "null" public class LambdaRequestHandlerTest { private LambdaRequestHandler handler; @Mock Context context; @Mock LambdaLogger loggerMock;

@Before
public void setUp() throws Exception {
  when(context.getLogger()).thenReturn(loggerMock);
    
  doAnswer(call -> {
        System.out.println((String)call.getArgument(0));//print to the console
        return null;
    }).when(loggerMock).log(anyString());
    
  handler = new LambdaRequestHandler();
}

@Test
public void handleRequest() {
    String respond = handler.handleRequest("some input", context);
}

}

//In the request handler public class LambdaRequestHandler implements RequestHandler<String, String> { @Override public String handleRequest(String input, Context context) { LambdaLogger logger = context.getLogger(); logger.log("some log message");

  return "some output";
}

}