Assert.AreEqual failing in unit test

Question

I have the following unit test:

string MtrlCode = "0";
Assessment target = new Assessment(MtrlCode);

List<string> EdgeCaseSymbolCodes = new List<string>(); //More than 3
EdgeCaseSymbolCodes.Add("FLA");
EdgeCaseSymbolCodes.Add("HAR");
EdgeCaseSymbolCodes.Add("COR");
EdgeCaseSymbolCodes.Add("ENVON");
EdgeCaseSymbolCodes.Add("ENVR");
EdgeCaseSymbolCodes.Add("EXP");

target.HazardSymbols = EdgeCaseSymbolCodes;

List<string> EdgeCaseSymbolCodesExpected = new List<string>(); //Should be 3
EdgeCaseSymbolCodesExpected.Add("FLA");
EdgeCaseSymbolCodesExpected.Add("HAR");
EdgeCaseSymbolCodesExpected.Add("COR");

System.Windows.Forms.MessageBox.Show(EdgeCaseSymbolCodesExpected[0] + EdgeCaseSymbolCodesExpected[1] + EdgeCaseSymbolCodesExpected[2] + " = \n" + target.HazardSymbols[0] + target.HazardSymbols[1] + target.HazardSymbols[2]);

Assert.AreEqual<List<string>>(EdgeCaseSymbolCodesExpected, target.HazardSymbols, "COSHH_2008.Custom_Classes.Assessment.setHazardSymbols Edge Case did not return the expected value.");

Which is testing an edge case (a time when the List<string> has more than 3 elements) with the desired output being the return of only the first 3.

Currently the test is failing and I've had to resort to using the MessageBox to see inside of the test (due to the breakpoints not being hit!).

From what I can see the elements are the same, however I realise there might be something else different with the List<string> object, but I can't see this as the breakpoints are never been hit.

I can't find the modules window in Visual Studio 2005.

What would your next steps be?

Answer 1

Use CollectionAssert.AreEqual().

Answer 2

If Assert.Equals uses the default comparer(no idea if it does) then this test will fail since List<T> uses referential equality by default.

If both lists have the same ordering you can use the linq extensionmethod Enumerable.SequenceEqual to test for element wise equality.

If you want to consider lists with the same elements equal even with different ordering you could use a.Intersect(b).Count()==a.Unit(b).Count() since there is no SetEqual extension method in Linq.

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And even if it compared by value why do you expect a list containing 3 elements to be equal to a list containing 6 elements?

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As a sidenote: Your naming conventions differ from the .net conventions. Usually local variable names start with lower case letters.

And I find the line target.HazardSymbols = EdgeCaseSymbolCodes; very strange. Does that mean you have a property of type List<T> with a public setter? I'd rather avoid those since that can lead to different objects using the same instance of a List which can have strange effects if they modify the list they own.