Can we use TestNG expectedExceptionsMessageRegExp to match the cause text?

Question

expectedExceptionsMessageRegExp is trying to match the detailMessage field. Can we match the cause text? i.e the text returned by Exception.getCause() ? This is because the detailMessage field gives very generic message and it will beat the purpose of the test case if expected message is matched with that text.

@Test(expectedExceptions = TestExecutionException.class, expectedExceptionsMessageRegExp = ".* HTTP 422.*")
public void test() throws Exception {
    ..
    //some code that produces TestExecutionException with the cause HTTP 422
    ..
}

The TestNG error is:

The exception was thrown with the wrong message: expected ".* HTTP 422.*" but got "Failed executing MessageExecutionTask"
    at org.testng.internal.Invoker.handleInvocationResults(Invoker.java:1481)
    at org.testng.internal.Invoker.invokeMethod(Invoker.java:754)
    at org.testng.internal.Invoker.invokeTestMethod(Invoker.java:901)
    at org.testng.internal.Invoker.invokeTestMethods(Invoker.java:1231)
    ... 16 more

Answer 1

TestNG relies on Reflection to instantiate your test class and then invoke the @Test method. So an exception from the @Test method would trigger an java.lang.reflect.InvocationTargetException whose getCause() actually results in the exception raised by the @Test method.

TestNG is designed to query the InvocationTargetException.getCause().getMessage() to get the error message of the exception that was raised and then try and match it using the regex that is supplied via the expectedExceptionsMessageRegExp attribute of the @Test annotation.

Here's an example that runs fine with TestNG 6.12

import org.testng.ITestResult;
import org.testng.annotations.AfterMethod;
import org.testng.annotations.Test;

public class TestClass {

    @Test(expectedExceptions = OldMonkException.class, expectedExceptionsMessageRegExp = ".* HTTP 422.*")
    public void test() throws Exception {
        throw new OldMonkException("Your have triggered a HTTP 422 error code.");
    }

    @AfterMethod
    public void afterTestMethod(ITestResult testResult) {
        String mname = testResult.getMethod().getMethodName() + " ";
        switch (testResult.getStatus()) {
            case ITestResult.SUCCESS:
                mname += "passed";
                break;
            case ITestResult.FAILURE:
                mname += "failed";
                break;
            case ITestResult.SKIP:
                mname += "skipped";
                break;
            default:
                mname += "";
        }
        System.err.println(mname);
    }

    public static class OldMonkException extends Exception {
        OldMonkException(String message) {
            super(message);
        }
    }
}