Assert.ThrowsException test fails when it does throw exception

Question

I'm using Microsoft.VisualStudio.TestTools.UnitTesting for unit testing.

I have this test which asserts that an exception was thrown and it is failing

[TestMethod]
public async Task ShouldThrowHttpExceptionIfPassedObjectIsNull()
{
    _mockLogger = new Mock<ILogger<DataService>>();

    // setup memoryCache
    object expected = null;
    _mockNullMemoryCache = MockMemoryCacheService.GetNullMemoryCache(expected);
    _mockSessionManagementService = new MockSessionManagementService();

    _ds = new DataService(
        _mockLogger.Object,
        _mockNullMemoryCache.Object,
        _mockSessionManagementService
    );
    Assert.ThrowsException<HttpException>(() => _ds.RetrieveFileData<object>(_incorrectFilePath, false));
}

When I debug it, the last line of code to run before it errors out and fails is this:

The exception ex is a system.invalidOperationException but that shouldn't matter because it throws an HttpException not matter what. Why is the test failing with the reason:

Test Name: ShouldThrowHttpExceptionIfPassedObjectIsNull Test FullName: xxx.xxx.xxx.xxx.ShouldThrowHttpExceptionIfPassedObjectIsNull Test Source: C:\Users\xxx\xxx.cs : line 88 Test Outcome: Failed Test Duration: 0:04:35.5251661

Result StackTrace: at xxxxxx.d__10.MoveNext() in C:\Users\xxx\xxx\xxx.cs:line 101 --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) Result Message: Assert.ThrowsException failed. No exception thrown. HttpException exception was expected.

EDIT The code then moves into this code block after the image:

else
                {
                    // Parsing issue
                    _logger.LogError(string.Format("Id={0}, Could not retrieve data from {1} : Malformed source data", _sessionManagementService.SessionId, url));
                    throw new HttpException(HttpStatusCode.InternalServerError, "Malformed source data", true);
                }

As it is throwing the HttpException above, it throws a DllNotFoundException.

Exception thrown: 'System.DllNotFoundException' in System.Private.CoreLib.ni.dll

Additional information: Unable to load DLL 'combase.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)

@ThomasWeller no but the test is testing for HttpException, which is the one that is thrown. — BeniaminoBaggins, Feb 23 '17 at 19:44

Thomas Weller · Accepted Answer · 2017-02-23T20:38:11.167

2

When I look at the type hierarchy of HttpException, I see that it doe not inherit from InvalidOperationException. Therefore the unit test fails correctly.

Likely there's some LINQ code or other code which cannot execute correctly, therefore catches the HttpException and converts it into the InvalidOperationException.

You should be able to debug the unit test. Instruct Visual Studio to stop at exceptions, then go forward step by step and try to find out where your exception gets converted, e.g. when you step through some LINQ code.

The MoveNext() call indicates that something tries to loop over values. When debugging, disable Just my code, because it could be in the .NET framework.

edited Feb 23 '17 at 20:38

answered Feb 23 '17 at 19:55

Thomas Weller

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But when I go forward step by step from the line of code in the image above, it just crashes after that line of code. – BeniaminoBaggins Feb 23 '17 at 20:10
Okay disregard my last comment. Doing that now. Thanks – BeniaminoBaggins Feb 23 '17 at 20:18
Your answer is the solution. Thanks!. I'm just wondering if you could point me in the right direction regarding what I found out (see the edit in the bottom of my question). It's strange because it throws the HttpException successfully the first time, although it has only 2 argument compared to 3 arguments in the last one. Maybe the code under test needs to be changed? – BeniaminoBaggins Feb 23 '17 at 20:30
A DllNotFoundException is something different again. Can you go on debugging? Is DllNotFoundException caught by something else once more? – Thomas Weller Feb 23 '17 at 20:42
Disregard my last comment. I forgot that _logger is mocked. I just need to keep working on this in solitude as you have help all you can from across the interwebs. Thanks for your help! – BeniaminoBaggins Feb 23 '17 at 20:50

Assert.ThrowsException test fails when it does throw exception

1 Answers1