WIP: Add DependsOnFixture example to dependent tests guide

docs/articles/nunit/writing-tests/dependent-tests.md

@@ -32,6 +32,21 @@ When a whole class of tests depends on another class, put [`[DependsOnFixture]`]
 the class, with the type of the fixture it depends on. It works the same way: the dependent fixture waits for the other
 fixture, and is skipped if that fixture fails, unless `AllowFailure` is set.
 
+[!code-csharp[DependentFixtures](~/snippets/Snippets.NUnit/DependentFixtureExamples.cs#DependentFixtures)]
+
+- `SeedDatabaseTests` has no dependency, so it runs first and fills the shared `CustomerDatabase`.
+- `CustomerReportTests` starts only after **all** tests in `SeedDatabaseTests` have finished. If any of them fails, the
+  fixture fails, and **every** test in `CustomerReportTests` is skipped, with a message that names the failed
+  dependency.
+- `CleanUpDatabaseTests` depends on `CustomerReportTests` with `AllowFailure = true`. It runs last, even if a report
+  test failed, so the shared data is always removed.
+- Dependencies chain: `CleanUpDatabaseTests` waits for `CustomerReportTests`, which waits for `SeedDatabaseTests`.
+  When you run only a dependent fixture, for example from your IDE, NUnit still includes the fixture it depends on.
+
+A fixture has at most one `[DependsOnFixture]`, and the fixture it names must be in the same namespace. A fixture in
+another namespace, or one that was not found in the run, makes the dependent fixture fail as invalid. A fixture can't
+depend on its own base class.
+
 ## Things to keep in mind
 
 - Tests in a dependency chain can't run in parallel with each other. Don't mark them

docs/snippets/Snippets.NUnit/DependentFixtureExamples.cs

@@ -0,0 +1,53 @@
+using NUnit.Framework;
+
+// Fixture dependencies are resolved between fixtures in the same namespace,
+// so these examples have their own namespace.
+namespace Snippets.NUnit.DependentFixtures;
+
+#region DependentFixtures
+// State shared between fixtures. Fixture dependencies make the order safe.
+public static class CustomerDatabase
+{
+    public static List<string> Customers { get; } = [];
+}
+
+public class SeedDatabaseTests
+{
+    [Test]
+    public void AddCustomers()
+    {
+        CustomerDatabase.Customers.AddRange(["Alice", "Bob"]);
+        Assert.That(CustomerDatabase.Customers, Has.Count.EqualTo(2));
+    }
+}
+
+[DependsOnFixture(typeof(SeedDatabaseTests))]
+public class CustomerReportTests
+{
+    // All tests in this fixture run after every test in SeedDatabaseTests.
+    // If SeedDatabaseTests fails, this whole fixture is skipped.
+    [Test]
+    public void Report_ListsAllCustomers()
+    {
+        Assert.That(CustomerDatabase.Customers, Is.EquivalentTo(new[] { "Alice", "Bob" }));
+    }
+
+    [Test]
+    public void Report_HasNoDuplicates()
+    {
+        Assert.That(CustomerDatabase.Customers, Is.Unique);
+    }
+}
+
+[DependsOnFixture(typeof(CustomerReportTests), AllowFailure = true)]
+public class CleanUpDatabaseTests
+{
+    // Runs after CustomerReportTests even if it failed, so the cleanup always happens.
+    [Test]
+    public void RemoveCustomers()
+    {
+        CustomerDatabase.Customers.Clear();
+        Assert.That(CustomerDatabase.Customers, Is.Empty);
+    }
+}
+#endregion