Order unit tests
Occasionally, you may want to have unit tests run in a specific order. Ideally, the order in which unit tests run should not matter, and it is best practice to avoid ordering unit tests. Regardless, there may be a need to do so. In that case, this article demonstrates how to order test runs.
If you prefer to browse the source code, see the order .NET Core unit tests sample repository.
Tip
In addition to the ordering capabilities outlined in this article, consider creating custom playlists with Visual Studio as an alternative.
Order alphabetically
With MSTest, tests are automatically ordered by their test name.
Note
A test named Test14 will run before Test2 even though the number 2 is less than 14. This is because test name ordering uses the text name of the test.
using Microsoft.VisualStudio.TestTools.UnitTesting;
namespace MSTest.Project;
[TestClass]
public class ByAlphabeticalOrder
{
public static bool Test1Called;
public static bool Test2Called;
public static bool Test3Called;
[TestMethod]
public void Test2()
{
Test2Called = true;
Assert.IsTrue(Test1Called);
Assert.IsFalse(Test3Called);
}
[TestMethod]
public void Test1()
{
Test1Called = true;
Assert.IsFalse(Test2Called);
Assert.IsFalse(Test3Called);
}
[TestMethod]
public void Test3()
{
Test3Called = true;
Assert.IsTrue(Test1Called);
Assert.IsTrue(Test2Called);
}
}
The xUnit test framework allows for more granularity and control of test run order. You implement the ITestCaseOrderer and ITestCollectionOrderer interfaces to control the order of test cases for a class, or test collections.
Order by test case alphabetically
To order test cases by their method name, you implement the ITestCaseOrderer and provide an ordering mechanism.
using Xunit.Abstractions;
using Xunit.Sdk;
namespace XUnit.Project.Orderers;
public class AlphabeticalOrderer : ITestCaseOrderer
{
public IEnumerable<TTestCase> OrderTestCases<TTestCase>(
IEnumerable<TTestCase> testCases) where TTestCase : ITestCase =>
testCases.OrderBy(testCase => testCase.TestMethod.Method.Name);
}
Then in a test class you set the test case order with the TestCaseOrdererAttribute.
using Xunit;
namespace XUnit.Project;
[TestCaseOrderer(
ordererTypeName: "XUnit.Project.Orderers.AlphabeticalOrderer",
ordererAssemblyName: "XUnit.Project")]
public class ByAlphabeticalOrder
{
public static bool Test1Called;
public static bool Test2Called;
public static bool Test3Called;
[Fact]
public void Test1()
{
Test1Called = true;
Assert.False(Test2Called);
Assert.False(Test3Called);
}
[Fact]
public void Test2()
{
Test2Called = true;
Assert.True(Test1Called);
Assert.False(Test3Called);
}
[Fact]
public void Test3()
{
Test3Called = true;
Assert.True(Test1Called);
Assert.True(Test2Called);
}
}
Order by collection alphabetically
To order test collections by their display name, you implement the ITestCollectionOrderer and provide an ordering mechanism.
using Xunit;
using Xunit.Abstractions;
namespace XUnit.Project.Orderers;
public class DisplayNameOrderer : ITestCollectionOrderer
{
public IEnumerable<ITestCollection> OrderTestCollections(
IEnumerable<ITestCollection> testCollections) =>
testCollections.OrderBy(collection => collection.DisplayName);
}
Since test collections potentially run in parallel, you must explicitly disable test parallelization of the collections with the CollectionBehaviorAttribute. Then specify the implementation to the TestCollectionOrdererAttribute.
using Xunit;
// Need to turn off test parallelization so we can validate the run order
[assembly: CollectionBehavior(DisableTestParallelization = true)]
[assembly: TestCollectionOrderer(
ordererTypeName: "XUnit.Project.Orderers.DisplayNameOrderer",
ordererAssemblyName: "XUnit.Project")]
namespace XUnit.Project;
[Collection("Xzy Test Collection")]
public class TestsInCollection1
{
public static bool Collection1Run;
[Fact]
public static void Test()
{
Assert.True(TestsInCollection2.Collection2Run); // Abc
Assert.True(TestsInCollection3.Collection3Run); // Mno
Assert.False(TestsInCollection1.Collection1Run); // Xyz
Collection1Run = true;
}
}
[Collection("Abc Test Collection")]
public class TestsInCollection2
{
public static bool Collection2Run;
[Fact]
public static void Test()
{
Assert.False(TestsInCollection2.Collection2Run); // Abc
Assert.False(TestsInCollection3.Collection3Run); // Mno
Assert.False(TestsInCollection1.Collection1Run); // Xyz
Collection2Run = true;
}
}
[Collection("Mno Test Collection")]
public class TestsInCollection3
{
public static bool Collection3Run;
[Fact]
public static void Test()
{
Assert.True(TestsInCollection2.Collection2Run); // Abc
Assert.False(TestsInCollection3.Collection3Run); // Mno
Assert.False(TestsInCollection1.Collection1Run); // Xyz
Collection3Run = true;
}
}
Order by custom attribute
To order xUnit tests with custom attributes, you first need an attribute to rely on. Define a TestPriorityAttribute as follows:
namespace XUnit.Project.Attributes;
[AttributeUsage(AttributeTargets.Method, AllowMultiple = false)]
public class TestPriorityAttribute : Attribute
{
public int Priority { get; private set; }
public TestPriorityAttribute(int priority) => Priority = priority;
}
Next, consider the following PriorityOrderer implementation of the ITestCaseOrderer interface.
using Xunit.Abstractions;
using Xunit.Sdk;
using XUnit.Project.Attributes;
namespace XUnit.Project.Orderers;
public class PriorityOrderer : ITestCaseOrderer
{
public IEnumerable<TTestCase> OrderTestCases<TTestCase>(
IEnumerable<TTestCase> testCases) where TTestCase : ITestCase
{
string assemblyName = typeof(TestPriorityAttribute).AssemblyQualifiedName!;
var sortedMethods = new SortedDictionary<int, List<TTestCase>>();
foreach (TTestCase testCase in testCases)
{
int priority = testCase.TestMethod.Method
.GetCustomAttributes(assemblyName)
.FirstOrDefault()
?.GetNamedArgument<int>(nameof(TestPriorityAttribute.Priority)) ?? 0;
GetOrCreate(sortedMethods, priority).Add(testCase);
}
foreach (TTestCase testCase in
sortedMethods.Keys.SelectMany(
priority => sortedMethods[priority].OrderBy(
testCase => testCase.TestMethod.Method.Name)))
{
yield return testCase;
}
}
private static TValue GetOrCreate<TKey, TValue>(
IDictionary<TKey, TValue> dictionary, TKey key)
where TKey : struct
where TValue : new() =>
dictionary.TryGetValue(key, out TValue? result)
? result
: (dictionary[key] = new TValue());
}
Then in a test class you set the test case order with the TestCaseOrdererAttribute to the PriorityOrderer.
using Xunit;
using XUnit.Project.Attributes;
namespace XUnit.Project;
[TestCaseOrderer(
ordererTypeName: "XUnit.Project.Orderers.PriorityOrderer",
ordererAssemblyName: "XUnit.Project")]
public class ByPriorityOrder
{
public static bool Test1Called;
public static bool Test2ACalled;
public static bool Test2BCalled;
public static bool Test3Called;
[Fact, TestPriority(5)]
public void Test3()
{
Test3Called = true;
Assert.True(Test1Called);
Assert.True(Test2ACalled);
Assert.True(Test2BCalled);
}
[Fact, TestPriority(0)]
public void Test2B()
{
Test2BCalled = true;
Assert.True(Test1Called);
Assert.True(Test2ACalled);
Assert.False(Test3Called);
}
[Fact]
public void Test2A()
{
Test2ACalled = true;
Assert.True(Test1Called);
Assert.False(Test2BCalled);
Assert.False(Test3Called);
}
[Fact, TestPriority(-5)]
public void Test1()
{
Test1Called = true;
Assert.False(Test2ACalled);
Assert.False(Test2BCalled);
Assert.False(Test3Called);
}
}
Order by priority
To order tests explicitly, NUnit provides an OrderAttribute. Tests with this attribute are started before tests without. The order value is used to determine the order to run the unit tests.
using NUnit.Framework;
namespace NUnit.Project;
public class ByOrder
{
public static bool Test1Called;
public static bool Test2ACalled;
public static bool Test2BCalled;
public static bool Test3Called;
[Test, Order(5)]
public void Test1()
{
Test1Called = true;
Assert.That(Test2ACalled, Is.False);
Assert.That(Test2BCalled, Is.True);
Assert.That(Test3Called, Is.True);
}
[Test, Order(0)]
public void Test2B()
{
Test2BCalled = true;
Assert.That(Test1Called, Is.False);
Assert.That(Test2ACalled, Is.False);
Assert.That(Test3Called, Is.True);
}
[Test]
public void Test2A()
{
Test2ACalled = true;
Assert.That(Test1Called, Is.True);
Assert.That(Test2BCalled, Is.True);
Assert.That(Test3Called, Is.True);
}
[Test, Order(-5)]
public void Test3()
{
Test3Called = true;
Assert.That(Test1Called, Is.False);
Assert.That(Test2ACalled, Is.False);
Assert.That(Test2BCalled, Is.False);
}
}
Next Steps
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