TDD nUnit multiple asserts for one method

Question

Using TDD first time in my life today. I am using nUnit.

I have one method, where I can insert multiple different inputs and check if result works.

I read that multiple asserts in one test is not a problem, and I really don't want to write new test for each input.

Example with multiple asserts:

 [TestFixture] public class TestClass { public Program test; [SetUp] public void Init() { test = new Program(); } [Test] public void Parse_SimpleValues_Calculated() { Assert.AreEqual(25, test.ParseCalculationString("5*5")); Assert.AreEqual(125, test.ParseCalculationString("5*5*5")); Assert.AreEqual(10, test.ParseCalculationString("5+5")); Assert.AreEqual(15, test.ParseCalculationString("5+5+5")); Assert.AreEqual(50, test.ParseCalculationString("5*5+5*5")); Assert.AreEqual(3, test.ParseCalculationString("5-1*2")); Assert.AreEqual(7, test.ParseCalculationString("7+1-1")); } }

But when something fails it is very hard to read which assert failed, I mean if you have them a lot, you have to go through all and find the right assert.

Is there any elegant way to show what input did we set if assert fails, instead of result and expected result?

Thank you.

In my opinion, you should have a different test for each test case. Your test should have one reason to fail: You made a change in the code that broke your test case. What if you change some of your parsing logic so that addition operations fail, but subtraction is fine? If you have one test case, it will fail for both addition and subtraction. — Daniel Mann
– Daniel Mann, Commented Aug 18, 2013 at 19:36

Jon Skeet · Accepted Answer · 2013-08-18 18:15:30Z

I mean if you have them a lot, so you have to go through all.

No you don't - you just look at the stack trace. If you're running the tests within an IDE, I find that that's easily good enough to work out which line failed.

That said, there is a (significantly) better way - parameterized tests with TestCaseAttribute. So for example:

[Test] [TestCase("5*5", 25)] [TestCase("5*5*5", 125)] [TestCase("5+5", 10)] // etc public void Parse_SimpleValues_Calculated(string input, int expectedOutput) { Assert.AreEqual(expectedOutput, test.ParseCalculationString(input)); }

Now your unit test runner will show you each test case separately, and you'll be able to see which one fails. Additionally, it will run all of the tests, even if an early one fails - so you don't end up fixing one only to find that the next one failed unexpectedly.

There's also TestCaseSourceAttribute for cases where you want to specify a collection of inputs separately - e.g. to use across multiple tests.

That is what I wanted wow you are genius. I didn't know how to ask for those parametrized tests. Thank you sir.
@JohnMathilda: Far from a genius - I've just been in the same boat myself :)

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