[Test Improver] Add unit tests for RetryAttribute

test/UnitTests/TestFramework.UnitTests/Attributes/RetryAttributeTests.cs

@@ -0,0 +1,175 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+#pragma warning disable MSTESTEXP // Experimental API
+
+using AwesomeAssertions;
+
+using TestFramework.ForTestingMSTest;
+
+namespace Microsoft.VisualStudio.TestPlatform.TestFramework.UnitTests.Attributes;
+
+/// <summary>
+/// Tests for <see cref="RetryAttribute"/> constructor validation and retry execution logic.
+/// </summary>
+public class RetryAttributeTests : TestContainer
+{
+    public void Constructor_WhenMaxRetryAttemptsIsZero_ThrowsArgumentOutOfRangeException()
+    {
+        Action act = static () => _ = new RetryAttribute(0);
+        act.Should().Throw<ArgumentOutOfRangeException>()
+            .WithParameterName("maxRetryAttempts");
+    }
+
+    public void Constructor_WhenMaxRetryAttemptsIsNegative_ThrowsArgumentOutOfRangeException()
+    {
+        Action act = static () => _ = new RetryAttribute(-1);
+        act.Should().Throw<ArgumentOutOfRangeException>()
+            .WithParameterName("maxRetryAttempts");
+    }
+
+    public void Constructor_WhenMaxRetryAttemptsIsOne_SetsMaxRetryAttempts()
+    {
+        var attribute = new RetryAttribute(1);
+        attribute.MaxRetryAttempts.Should().Be(1);
+    }
+
+    public void Constructor_WhenMaxRetryAttemptsIsPositive_SetsMaxRetryAttempts()
+    {
+        var attribute = new RetryAttribute(5);
+        attribute.MaxRetryAttempts.Should().Be(5);
+    }
+
+    public void BackoffType_DefaultsToConstant()
+    {
+        var attribute = new RetryAttribute(2);
+        attribute.BackoffType.Should().Be(DelayBackoffType.Constant);
+    }
+
+    public void BackoffType_WhenSetToInvalidValue_ThrowsArgumentOutOfRangeException()
+    {
+        var attribute = new RetryAttribute(2);
+        Action act = () => attribute.BackoffType = (DelayBackoffType)99;
+        act.Should().Throw<ArgumentOutOfRangeException>()
+            .WithParameterName("value");
+    }
+
+    public void BackoffType_WhenSetToExponential_Succeeds()
+    {
+        RetryAttribute attribute = new(2) { BackoffType = DelayBackoffType.Exponential };
+        attribute.BackoffType.Should().Be(DelayBackoffType.Exponential);
+    }
+
+    public void MillisecondsDelayBetweenRetries_DefaultsToZero()
+    {
+        var attribute = new RetryAttribute(2);
+        attribute.MillisecondsDelayBetweenRetries.Should().Be(0);
+    }
+
+    public async Task ExecuteAsync_WhenTestPassesOnFirstRetry_StopsRetryingEarly()
+    {
+        var attribute = new RetryAttribute(maxRetryAttempts: 5);
+        int callCount = 0;
+
+        var passResult = new TestResult { Outcome = UnitTestOutcome.Passed };
+        var failResult = new TestResult { Outcome = UnitTestOutcome.Failed };
+
+        TestResult[] firstRunResults = [failResult];
+        var context = new RetryContext(
+            () =>
+            {
+                callCount++;
+                return Task.FromResult(new[] { passResult });
+            },
+            firstRunResults);
+
+        RetryResult result = await attribute.ExecuteAsync(context);
+
+        callCount.Should().Be(1);
+        result.TryGetLast().Should().ContainSingle()
+            .Which.Outcome.Should().Be(UnitTestOutcome.Passed);
+    }
+
+    public async Task ExecuteAsync_WhenAllRetriesFail_ExecutesExactlyMaxRetryAttemptsTimes()
+    {
+        var attribute = new RetryAttribute(maxRetryAttempts: 3);
+        int callCount = 0;
+
+        var failResult = new TestResult { Outcome = UnitTestOutcome.Failed };
+        TestResult[] firstRunResults = [failResult];
+
+        var context = new RetryContext(
+            () =>
+            {
+                callCount++;
+                return Task.FromResult(new[] { new TestResult { Outcome = UnitTestOutcome.Failed } });
+            },
+            firstRunResults);
+
+        await attribute.ExecuteAsync(context);
+
+        callCount.Should().Be(3);
+    }
+
+    public async Task ExecuteAsync_WhenAllRetriesFail_ResultContainsLastAttemptOutcome()
+    {
+        var attribute = new RetryAttribute(maxRetryAttempts: 2);
+        int callCount = 0;
+
+        TestResult[] firstRunResults = [new TestResult { Outcome = UnitTestOutcome.Failed }];
+        var context = new RetryContext(
+            () =>
+            {
+                callCount++;
+                UnitTestOutcome outcome = callCount == 2 ? UnitTestOutcome.Timeout : UnitTestOutcome.Failed;
+                return Task.FromResult(new[] { new TestResult { Outcome = outcome } });
+            },
+            firstRunResults);
+
+        RetryResult result = await attribute.ExecuteAsync(context);
+
+        result.TryGetLast().Should().ContainSingle()
+            .Which.Outcome.Should().Be(UnitTestOutcome.Timeout);
+    }
+
+    public async Task ExecuteAsync_WhenTestPassesAfterSeveralFailures_StopsAtFirstSuccess()
+    {
+        var attribute = new RetryAttribute(maxRetryAttempts: 5);
+        int callCount = 0;
+
+        TestResult[] firstRunResults = [new TestResult { Outcome = UnitTestOutcome.Failed }];
+        var context = new RetryContext(
+            () =>
+            {
+                callCount++;
+                UnitTestOutcome outcome = callCount < 3 ? UnitTestOutcome.Failed : UnitTestOutcome.Passed;
+                return Task.FromResult(new[] { new TestResult { Outcome = outcome } });
+            },
+            firstRunResults);
+
+        RetryResult result = await attribute.ExecuteAsync(context);
+
+        callCount.Should().Be(3);
+        result.TryGetLast().Should().ContainSingle()
+            .Which.Outcome.Should().Be(UnitTestOutcome.Passed);
+    }
+
+    public async Task ExecuteAsync_WhenResultIsInconclusive_StopsRetrying()
+    {
+        var attribute = new RetryAttribute(maxRetryAttempts: 5);
+        int callCount = 0;
+
+        TestResult[] firstRunResults = [new TestResult { Outcome = UnitTestOutcome.Failed }];
+        var context = new RetryContext(
+            () =>
+            {
+                callCount++;
+                return Task.FromResult(new[] { new TestResult { Outcome = UnitTestOutcome.Inconclusive } });
+            },
+            firstRunResults);
+
+        await attribute.ExecuteAsync(context);
+
+        callCount.Should().Be(1);
+    }
+}