Does NUnit provide a constraint to find whether the actual value is the element of a given enumerable or array, in other words, that it is equal to any of multiple expected values? Something like:
Assert.That(actual, Is.EqualToAnyOf(new[] { 1, 2, 3 }))
That is, to point out, the actual is a single value. I expect the value to be either 1
, 2
, or 3
. The assertion
Assert.That(actual, Contains.Element(expected))
checks logically the same, but it is the opposite intention: Here we have a collection of actual values and expect one value to be in it.
Furthermore, I found these but they all don't fit:
Assert.That(actual, Is.EqualTo(expected)) // only allows one value
Assert.That(actual, Is.InRange(start, end)) // only works for consecutive numbers
Assert.That(actual, Is.SubsetOf(expected)) // only works if actual is an enumerable
Assert.That(expected.Contains(actual)) // meaningless "expected: true but was: false" message
CollectionAssert should be what you need if I am not overlooking something. It is as simple as:
CollectionAssert.Contains(IEnumerable expected, object actual);
However, there seems to be several ways to achieve your goal, such as:
[Test]
public void CollectionContains()
{
var expected = new List<int> { 0, 1, 2, 3, 5 };
var actual = 5;
CollectionAssert.Contains(expected, actual);
Assert.That(expected, Contains.Item(actual));
}
Above assertions should basically assert the same and could be used interchangeably.
Edit: Question was modified, stating that Assert.That(expected, Contains.Item(actual));
is not valid even though it logically tests the same thing.
There is a way to do this built in to NUnit, using the Or
constraint:
Assert.That(actual, Is.EqualTo(1).Or.EqualTo(2).Or.EqualTo(3))
If your list is more dynamic, you can build your list of Or
s like this:
var expected = new[] { 1, 2, 3 };
var constraints = Is.EqualTo(expected[0]);
for(var i = 1; i < expected.Length; i++)
constraints = constraints.Or.EqualTo(expected[i]);
Assert.That(actual, constraints);
That latter answer doesn't read as well in the fluid syntax, but does achieve the dynamic building of or constraints. You could probably wrap that in a custom constraint as patrick-quirk demonstrated in order to achieve a more readbale fluid syntax, but that's up to you.
The only way I could see to accomplish this is by creating your own constraint. It's pretty straightforward to do though.
The constraint class itself:
public class OneOfValuesConstraint : EqualConstraint
{
readonly ICollection expected;
NUnitEqualityComparer comparer = new NUnitEqualityComparer();
public OneOfValuesConstraint(ICollection expected)
: base(expected)
{
this.expected = expected;
}
public override bool Matches(object actual)
{
// set the base class value so it appears in the error message
this.actual = actual;
Tolerance tolerance = Tolerance.Empty;
// Loop through the expected values and return true on first match
foreach (object value in expected)
if (comparer.AreEqual(value, actual, ref tolerance))
return true;
// No matches, return false
return false;
}
// Overridden for a cleaner error message (contributed by @chiccodoro)
public override void WriteMessageTo(MessageWriter writer)
{
writer.DisplayDifferences(this);
}
public override void WriteDescriptionTo(MessageWriter writer)
{
writer.Write("either of ");
writer.WriteExpectedValue(this.expected);
}
}
And to make it fluent, create a static method to wrap it (contributed by @chicodorro):
public static class IsEqual
{
public static OneOfValuesConstraint ToAny(ICollection expected)
{
return new OneOfValuesConstraint(expected);
}
}
Then to use it:
int[] expectedValues = new[] { 0, 1, 2 };
Assert.That(6, IsEqual.ToAny(expectedValues));
Fails with the message:
Expected: either of < 0, 1, 2 >
But was: 6
I know this is an old question, bu I have a maybe better (and native) suggestion. With NUnit 3.x (I'm on 3.10.1) you can use Is.AnyOf :
Assert.That(
actualValue,
Is.AnyOf(expectedValue1, expectedValue2, expectedValue3),
"My error message");
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