ValueSource

ValueSourceAttribute is used on individual parameters of a test method to identify a named data source for argument values.

Constructors

ValueSourceAttribute(Type sourceType, string sourceName)
ValueSourceAttribute(string sourceName)
Parameter Type Description
sourceType Type Type that provides the source member. Optional.
sourceName string Name of source field, property, or method.

Applies To

Method Parameters Test Methods Test Fixtures (Classes) Assembly
✅ ❌ ❌ ❌

Example

[Test]
public void TestUsingValueSource([ValueSource(nameof(Numbers))] int value)
{
    Assert.That(value, Is.GreaterThan(0));
}

Source Requirements

  • Source may be a field, non-indexed property, or parameterless method.
  • Source member must be static.
  • Source must return IEnumerable (or async forms supported by NUnit).
  • Returned items must be compatible with the annotated parameter type.

Order of Execution

Individual test cases are executed in the order in which NUnit discovers them. This order does not follow the lexical order of the attributes and will often vary between different compilers or different versions of the CLR.

As a result, when ValueSourceAttribute appears multiple times on a parameter or when other data-providing attributes are used in combination with ValueSourceAttribute, the order of the arguments is undefined.

However, when a single ValueSourceAttribute is used by itself, the order of the arguments follows exactly the order in which the data is returned from the source.

Note on Object Construction

NUnit locates the test cases at the time the tests are loaded, creates instances of each class with non-static sources and builds a list of tests to be executed. Each source object is only created once at this time and is destroyed after all tests are loaded.

If the data source is in the test fixture itself, the object is created using the appropriate constructor for the fixture parameters provided on the TestFixtureAttribute, or the default constructor if no parameters were specified. Since this object is destroyed before the tests are run, no communication is possible between these two phases - or between different runs - except through the parameters themselves.

See Also