feat: add TestContext.Isolation interface for test resource isolation

TUnit.AspNetCore/WebApplicationTest.cs

@@ -10,17 +10,15 @@ namespace TUnit.AspNetCore;
 
 public abstract class WebApplicationTest
 {
-    internal static int _idCounter;
-
     /// <summary>
     /// Gets a unique identifier for this test instance.
-    /// Useful for creating isolated resources (tables, topics, keys) per test.
+    /// Delegates to <see cref="TestContext.Isolation"/> to ensure consistency
+    /// regardless of whether accessed via this property or the TestContext API.
     /// </summary>
-    public int UniqueId { get; }
+    public int UniqueId => TestContext.Current!.Isolation.UniqueId;
 
     internal WebApplicationTest()
     {
-        UniqueId = Interlocked.Increment(ref _idCounter);
     }
 
     /// <summary>
@@ -36,7 +34,7 @@ internal WebApplicationTest()
     /// var topicName = GetIsolatedName("orders"); // Returns "Test_42_orders"
     /// </code>
     /// </example>
-    protected string GetIsolatedName(string baseName) => $"Test_{UniqueId}_{baseName}";
+    protected string GetIsolatedName(string baseName) => TestContext.Current!.Isolation.GetIsolatedName(baseName);
 
     /// <summary>
     /// Creates an isolated prefix using the test's unique identifier.
@@ -51,7 +49,7 @@ internal WebApplicationTest()
     /// var dotPrefix = GetIsolatedPrefix("."); // Returns "test.42."
     /// </code>
     /// </example>
-    protected string GetIsolatedPrefix(string separator = "_") => $"test{separator}{UniqueId}{separator}";
+    protected string GetIsolatedPrefix(string separator = "_") => TestContext.Current!.Isolation.GetIsolatedPrefix(separator);
 }
 
 /// <summary>

TUnit.Core/Interfaces/ITestIsolation.cs

@@ -0,0 +1,46 @@
+namespace TUnit.Core.Interfaces;
+
+/// <summary>
+/// Provides helpers for creating isolated resource names per test instance.
+/// Useful for database tables, queue names, cache keys, and other resources
+/// that need to be unique across parallel test execution.
+/// Accessed via <see cref="TestContext.Isolation"/>.
+/// </summary>
+public interface ITestIsolation
+{
+    /// <summary>
+    /// Gets a unique identifier for this test instance.
+    /// This value is assigned atomically and is guaranteed to be unique across all test instances in the process.
+    /// </summary>
+    int UniqueId { get; }
+
+    /// <summary>
+    /// Creates an isolated name by combining a base name with the test's unique identifier.
+    /// Use for database tables, Redis keys, Kafka topics, etc.
+    /// </summary>
+    /// <param name="baseName">The base name for the resource.</param>
+    /// <returns>A unique name in the format "Test_{UniqueId}_{baseName}".</returns>
+    /// <example>
+    /// <code>
+    /// // In a test with UniqueId = 42:
+    /// var tableName = TestContext.Current!.Isolation.GetIsolatedName("todos");  // Returns "Test_42_todos"
+    /// var topicName = TestContext.Current!.Isolation.GetIsolatedName("orders"); // Returns "Test_42_orders"
+    /// </code>
+    /// </example>
+    string GetIsolatedName(string baseName);
+
+    /// <summary>
+    /// Creates an isolated prefix using the test's unique identifier.
+    /// Use for key prefixes in Redis, Kafka topic prefixes, etc.
+    /// </summary>
+    /// <param name="separator">The separator character. Defaults to "_".</param>
+    /// <returns>A unique prefix in the format "test{separator}{UniqueId}{separator}".</returns>
+    /// <example>
+    /// <code>
+    /// // In a test with UniqueId = 42:
+    /// var prefix = TestContext.Current!.Isolation.GetIsolatedPrefix();       // Returns "test_42_"
+    /// var dotPrefix = TestContext.Current!.Isolation.GetIsolatedPrefix("."); // Returns "test.42."
+    /// </code>
+    /// </example>
+    string GetIsolatedPrefix(string separator = "_");
+}

TUnit.Core/TestContext.Isolation.cs

@@ -0,0 +1,19 @@
+using TUnit.Core.Interfaces;
+
+namespace TUnit.Core;
+
+public partial class TestContext
+{
+    internal static int _isolationIdCounter;
+
+    internal int IsolationUniqueId { get; }
+
+    /// <inheritdoc/>
+    int ITestIsolation.UniqueId => IsolationUniqueId;
+
+    /// <inheritdoc/>
+    string ITestIsolation.GetIsolatedName(string baseName) => $"Test_{IsolationUniqueId}_{baseName}";
+
+    /// <inheritdoc/>
+    string ITestIsolation.GetIsolatedPrefix(string separator) => $"test{separator}{IsolationUniqueId}{separator}";
+}

TUnit.Core/TestContext.cs

@@ -15,7 +15,7 @@ namespace TUnit.Core;
 /// </summary>
 [DebuggerDisplay("{TestDetails.ClassType.Name}.{GetDisplayName(),nq}")]
 public partial class TestContext : Context,
-    ITestExecution, ITestParallelization, ITestOutput, ITestMetadata, ITestDependencies, ITestStateBag, ITestEvents
+    ITestExecution, ITestParallelization, ITestOutput, ITestMetadata, ITestDependencies, ITestStateBag, ITestEvents, ITestIsolation
 {
     private static readonly ConcurrentDictionary<string, TestContext> _testContextsById = new();
     private readonly TestBuilderContext _testBuilderContext;
@@ -30,6 +30,7 @@ public TestContext(string testName, IServiceProvider serviceProvider, ClassHookC
 
         // Generate unique ID for this test instance
         Id = Guid.NewGuid().ToString();
+        IsolationUniqueId = Interlocked.Increment(ref _isolationIdCounter);
 
         _testContextsById[Id] = this;
     }
@@ -44,6 +45,7 @@ public TestContext(string testName, IServiceProvider serviceProvider, ClassHookC
     public ITestDependencies Dependencies => this;
     public ITestStateBag StateBag => this;
     public ITestEvents Events => this;
+    public ITestIsolation Isolation => this;
 
     internal IServiceProvider Services => ServiceProvider;
 

TUnit.PublicAPI/Tests.Core_Library_Has_No_API_Changes.DotNet10_0.verified.txt

@@ -1327,14 +1327,15 @@ namespace
         public TestConstructorAttribute() { }
     }
     [.DebuggerDisplay("{.Name}.{GetDisplayName(),nq}")]
-    public class TestContext : .Context, ., ., ., ., ., ., .
+    public class TestContext : .Context, ., ., ., ., ., ., ., .
     {
         public TestContext(string testName,  serviceProvider, .ClassHookContext classContext, .TestBuilderContext testBuilderContext, .CancellationToken cancellationToken) { }
         public .ClassHookContext ClassContext { get; }
         public . Dependencies { get; }
         public . Events { get; }
         public . Execution { get; }
         public string Id { get; }
+        public . Isolation { get; }
         public object Lock { get; }
         public . Metadata { get; }
         public . Output { get; }
@@ -2477,6 +2478,12 @@ namespace .Interfaces
         string TestId { get; }
         string TestName { get; }
     }
+    public interface ITestIsolation
+    {
+        int UniqueId { get; }
+        string GetIsolatedName(string baseName);
+        string GetIsolatedPrefix(string separator = "_");
+    }
     public interface ITestLocation
     {
         string TestFilePath { get; }

TUnit.PublicAPI/Tests.Core_Library_Has_No_API_Changes.DotNet8_0.verified.txt

@@ -1327,14 +1327,15 @@ namespace
         public TestConstructorAttribute() { }
     }
     [.DebuggerDisplay("{.Name}.{GetDisplayName(),nq}")]
-    public class TestContext : .Context, ., ., ., ., ., ., .
+    public class TestContext : .Context, ., ., ., ., ., ., ., .
     {
         public TestContext(string testName,  serviceProvider, .ClassHookContext classContext, .TestBuilderContext testBuilderContext, .CancellationToken cancellationToken) { }
         public .ClassHookContext ClassContext { get; }
         public . Dependencies { get; }
         public . Events { get; }
         public . Execution { get; }
         public string Id { get; }
+        public . Isolation { get; }
         public object Lock { get; }
         public . Metadata { get; }
         public . Output { get; }
@@ -2477,6 +2478,12 @@ namespace .Interfaces
         string TestId { get; }
         string TestName { get; }
     }
+    public interface ITestIsolation
+    {
+        int UniqueId { get; }
+        string GetIsolatedName(string baseName);
+        string GetIsolatedPrefix(string separator = "_");
+    }
     public interface ITestLocation
     {
         string TestFilePath { get; }

TUnit.PublicAPI/Tests.Core_Library_Has_No_API_Changes.DotNet9_0.verified.txt

@@ -1327,14 +1327,15 @@ namespace
         public TestConstructorAttribute() { }
     }
     [.DebuggerDisplay("{.Name}.{GetDisplayName(),nq}")]
-    public class TestContext : .Context, ., ., ., ., ., ., .
+    public class TestContext : .Context, ., ., ., ., ., ., ., .
     {
         public TestContext(string testName,  serviceProvider, .ClassHookContext classContext, .TestBuilderContext testBuilderContext, .CancellationToken cancellationToken) { }
         public .ClassHookContext ClassContext { get; }
         public . Dependencies { get; }
         public . Events { get; }
         public . Execution { get; }
         public string Id { get; }
+        public . Isolation { get; }
         public object Lock { get; }
         public . Metadata { get; }
         public . Output { get; }
@@ -2477,6 +2478,12 @@ namespace .Interfaces
         string TestId { get; }
         string TestName { get; }
     }
+    public interface ITestIsolation
+    {
+        int UniqueId { get; }
+        string GetIsolatedName(string baseName);
+        string GetIsolatedPrefix(string separator = "_");
+    }
     public interface ITestLocation
     {
         string TestFilePath { get; }

TUnit.PublicAPI/Tests.Core_Library_Has_No_API_Changes.Net4_7.verified.txt

@@ -1281,14 +1281,15 @@ namespace
         public TestConstructorAttribute() { }
     }
     [.DebuggerDisplay("{.Name}.{GetDisplayName(),nq}")]
-    public class TestContext : .Context, ., ., ., ., ., ., .
+    public class TestContext : .Context, ., ., ., ., ., ., ., .
     {
         public TestContext(string testName,  serviceProvider, .ClassHookContext classContext, .TestBuilderContext testBuilderContext, .CancellationToken cancellationToken) { }
         public .ClassHookContext ClassContext { get; }
         public . Dependencies { get; }
         public . Events { get; }
         public . Execution { get; }
         public string Id { get; }
+        public . Isolation { get; }
         public object Lock { get; }
         public . Metadata { get; }
         public . Output { get; }
@@ -2427,6 +2428,12 @@ namespace .Interfaces
         string TestId { get; }
         string TestName { get; }
     }
+    public interface ITestIsolation
+    {
+        int UniqueId { get; }
+        string GetIsolatedName(string baseName);
+        string GetIsolatedPrefix(string separator = "_");
+    }
     public interface ITestLocation
     {
         string TestFilePath { get; }

TUnit.UnitTests/TestIsolationTests.cs

@@ -0,0 +1,114 @@
+using TUnit.Assertions.Extensions;
+using TUnit.Core.Interfaces;
+
+namespace TUnit.UnitTests;
+
+public class TestIsolationTests
+{
+    [Test]
+    public async Task UniqueId_IsPositive()
+    {
+        var isolation = TestContext.Current!.Isolation;
+
+        await Assert.That(isolation.UniqueId).IsGreaterThan(0);
+    }
+
+    [Test]
+    public async Task UniqueId_IsDifferentAcrossTests_1()
+    {
+        // Store uniqueId in state bag so a parallel test can verify it's different
+        var isolation = TestContext.Current!.Isolation;
+        TestContext.Current.StateBag["isolation_test_id_1"] = isolation.UniqueId;
+
+        await Assert.That(isolation.UniqueId).IsGreaterThan(0);
+    }
+
+    [Test]
+    public async Task UniqueId_IsDifferentAcrossTests_2()
+    {
+        var isolation = TestContext.Current!.Isolation;
+        TestContext.Current.StateBag["isolation_test_id_2"] = isolation.UniqueId;
+
+        await Assert.That(isolation.UniqueId).IsGreaterThan(0);
+    }
+
+    [Test]
+    public async Task GetIsolatedName_ReturnsExpectedFormat()
+    {
+        var isolation = TestContext.Current!.Isolation;
+        var id = isolation.UniqueId;
+
+        var name = isolation.GetIsolatedName("foo");
+
+        await Assert.That(name).IsEqualTo($"Test_{id}_foo");
+    }
+
+    [Test]
+    public async Task GetIsolatedName_WithDifferentBaseNames_ReturnsDifferentNames()
+    {
+        var isolation = TestContext.Current!.Isolation;
+
+        var name1 = isolation.GetIsolatedName("todos");
+        var name2 = isolation.GetIsolatedName("orders");
+
+        await Assert.That(name1).IsNotEqualTo(name2);
+        await Assert.That(name1).Contains("todos");
+        await Assert.That(name2).Contains("orders");
+    }
+
+    [Test]
+    public async Task GetIsolatedPrefix_WithDefaultSeparator_ReturnsExpectedFormat()
+    {
+        var isolation = TestContext.Current!.Isolation;
+        var id = isolation.UniqueId;
+
+        var prefix = isolation.GetIsolatedPrefix();
+
+        await Assert.That(prefix).IsEqualTo($"test_{id}_");
+    }
+
+    [Test]
+    public async Task GetIsolatedPrefix_WithDotSeparator_ReturnsExpectedFormat()
+    {
+        var isolation = TestContext.Current!.Isolation;
+        var id = isolation.UniqueId;
+
+        var prefix = isolation.GetIsolatedPrefix(".");
+
+        await Assert.That(prefix).IsEqualTo($"test.{id}.");
+    }
+
+    [Test]
+    public async Task GetIsolatedPrefix_WithCustomSeparator_ReturnsExpectedFormat()
+    {
+        var isolation = TestContext.Current!.Isolation;
+        var id = isolation.UniqueId;
+
+        var prefix = isolation.GetIsolatedPrefix("-");
+
+        await Assert.That(prefix).IsEqualTo($"test-{id}-");
+    }
+
+    [Test]
+    public async Task Isolation_IsAccessibleViaInterface()
+    {
+        ITestIsolation isolation = TestContext.Current!.Isolation;
+
+        await Assert.That(isolation).IsNotNull();
+        await Assert.That(isolation.UniqueId).IsGreaterThan(0);
+    }
+
+    [Test]
+    public async Task Isolation_SameContextReturnsSameValues()
+    {
+        var context = TestContext.Current!;
+
+        var id1 = context.Isolation.UniqueId;
+        var id2 = context.Isolation.UniqueId;
+        var name1 = context.Isolation.GetIsolatedName("test");
+        var name2 = context.Isolation.GetIsolatedName("test");
+
+        await Assert.That(id1).IsEqualTo(id2);
+        await Assert.That(name1).IsEqualTo(name2);
+    }
+}

docs/docs/examples/aspnet.md

@@ -241,6 +241,10 @@ protected override void ConfigureWebHostBuilder(IWebHostBuilder builder)
 
 ## Test Isolation Helpers
 
+:::tip Available on All Tests
+The isolation helpers (`UniqueId`, `GetIsolatedName`, `GetIsolatedPrefix`) are also available on `TestContext.Current!.Isolation` for any test — not just ASP.NET Core tests. Use `TestContext.Current!.Isolation.GetIsolatedName("resource")` when you don't inherit from `WebApplicationTest`. Both share the same counter, so IDs are unique across all test types.
+:::
+
 ### GetIsolatedName
 
 Creates a unique name for resources like database tables: