NUnit parameterized tests with datetime

Is it not possible with NUnit to go the following?

[TestCase(new DateTime(2010,7,8), true)]
public void My Test(DateTime startdate, bool expectedResult)
{
    ...
}

I really want to put a datetime in there, but it doesn't seem to like it. The error is:

> An attribute argument must be a constant expression, typeof expression > or array creation expression of an attribute parameter type

Some documentation I read seems to suggest you should be able to, but I can't find any examples.

You can specify the date as a constant string in the TestCase attribute and then specify the type as DateTime in the method signature.

NUnit will automatically do a DateTime.Parse() on the string passed in.

Example:

[TestCase("01/20/2012")]
[TestCase("2012-1-20")] // Same case as above in ISO 8601 format
public void TestDate(DateTime dt)
{
    Assert.That(dt, Is.EqualTo(new DateTime(2012, 01, 20)));
}

I'd probably use something like the ValueSource attribute to do this:

public class TestData
{
    public DateTime StartDate{ get; set; }
    public bool ExpectedResult{ get; set; }
}

private static TestData[] _testData = new[]{
    new TestData(){StartDate= new DateTime(2010, 7, 8), ExpectedResult= true}};

[Test]
public void TestMethod([ValueSource("_testData")]TestData testData)
{
}

This will run the TestMethod for each entry in the _testData collection.

Another alternative is to use a more verbose approach. Especially if I don't necessarily know up front, what kind of DateTime() (if any...) a given string input yields.

[TestCase(2015, 2, 23)]
[TestCase(2015, 12, 3)]
public void ShouldCheckSomething(int year, int month, int day)
{
    var theDate = new DateTime(year,month,day);
    ....
} 

...note TestCase supports max 3 params so if you need more, consider something like:

private readonly object[] testCaseInput =
{
    new object[] { 2000, 1, 1, true, "first", true },
    new object[] { 2000, 1, 1, false, "second", false }
}

[Test, TestCaseSource("testCaseInput")]
public void Should_check_stuff(int y, int m, int d, bool condition, string theString, bool result)
{
....
}

You should use the TestCaseData Class as documented: http://www.nunit.org/index.php?p=testCaseSource&r=2.5.9

In addition to specifying an expected result, like:

 new TestCaseData(12, 4).Returns(3);

You can also specify expected exceptions, etc.:

 new TestCaseData(0, 0)
    .Throws(typeof(DivideByZeroException))
    .SetName("DivideByZero")
    .SetDescription("An exception is expected");

It seems that NUnit doesn't allow the initialization of non-primitive objects in the TestCase(s). It is best to use TestCaseData.

Your test data class would look like this:

public class DateTimeTestData
{
    public static IEnumerable GetDateTimeTestData()
    {
        // If you want past days.
        yield return new TestCaseData(DateTime.Now.AddDays(-1)).Returns(false);
        // If you want current time.
        yield return new TestCaseData(DateTime.Now).Returns(true);
        // If you want future days.
        yield return new TestCaseData(DateTime.Now.AddDays(1)).Returns(true);
    }
}

In your testing class you'd have the test include a TestCaseSource which directs to your test data.

How to use: TestCaseSource(typeof(class name goes here), nameof(name of property goes here))

[Test, TestCaseSource(typeof(DateTimeTestData), nameof(GetDateTimeTestData))]
public bool GetDateTime_GivenDateTime_ReturnsBoolean()
{
    // Arrange - Done in your TestCaseSource

    // Act
    // Method name goes here.

    // Assert
    // You just return the result of the method as this test uses ExpectedResult.
}

Nunit has improved and implicitly tries to convert the attribute arguments. See doc: NUnit3 Doc - see note

This works:

[TestCase("2021.2.1", ExpectedResult = false)]
[TestCase("2021.2.26", ExpectedResult = true)]
public bool IsDate(DateTime date) => date.Date.Equals(new DateTime(2021, 2, 26));

Take care to use english culture format for DateTime string arguments.