Avoid unnecessary testhost restarts.

src/coverlet.MTP/Collector/CollectorExtension.cs

@@ -40,9 +40,11 @@ internal sealed class CollectorExtension : ITestHostProcessLifetimeHandler, ITes
   private ICoverage? _coverage;
   private readonly Microsoft.Testing.Platform.Logging.ILoggerFactory _loggerFactory;
   private readonly Microsoft.Testing.Platform.CommandLine.ICommandLineOptions _commandLineOptions;
-  private bool _coverageEnabled;
   private string? _testModulePath;
   private string? _coverageIdentifier;
+  private bool? _isCoverageEnabled;
+
+  private bool IsCoverageEnabled => _isCoverageEnabled ??= _commandLineOptions.IsOptionSet(CoverletOptionNames.Coverage);
 
   private readonly CoverletExtension _extension = new();
   private readonly IReporterFactory _reporterFactory;
@@ -93,10 +95,9 @@ Task ITestHostProcessLifetimeHandler.BeforeTestHostProcessStartAsync(Cancellatio
     try
     {
       // Check if --coverlet flag was provided
-      _coverageEnabled = _commandLineOptions.IsOptionSet(CoverletOptionNames.Coverage);
-      _logger.LogVerbose($"Coverage enabled (--{CoverletOptionNames.Coverage} flag): {_coverageEnabled}");
+      _logger.LogVerbose($"Coverage enabled (--{CoverletOptionNames.Coverage} flag): {IsCoverageEnabled}");
 
-      if (!_coverageEnabled)
+      if (!IsCoverageEnabled)
       {
         _logger.LogInformation("Coverage collection is disabled. Use --coverlet to enable.");
         return Task.CompletedTask;
@@ -107,7 +108,7 @@ Task ITestHostProcessLifetimeHandler.BeforeTestHostProcessStartAsync(Cancellatio
       if (string.IsNullOrEmpty(_testModulePath))
       {
         _logger.LogError("Could not determine test module path. Coverage disabled.");
-        _coverageEnabled = false;
+        _isCoverageEnabled = false;
         return Task.CompletedTask;
       }
 
@@ -156,7 +157,7 @@ Task ITestHostProcessLifetimeHandler.BeforeTestHostProcessStartAsync(Cancellatio
     {
       _logger.LogError("Failed to initialize coverage instrumentation");
       _logger.LogError(ex);
-      _coverageEnabled = false;
+      _isCoverageEnabled = false;
 
       // Display error to user via IOutputDevice (visible in console output)
       DisplayErrorToUserAsync(ex).ConfigureAwait(false).GetAwaiter().GetResult();
@@ -234,7 +235,7 @@ private static string GetConciseErrorMessage(Exception ex)
   /// </summary>
   Task ITestHostEnvironmentVariableProvider.UpdateAsync(IEnvironmentVariables environmentVariables)
   {
-    if (_coverageEnabled && !string.IsNullOrEmpty(_coverageIdentifier))
+    if (IsCoverageEnabled && !string.IsNullOrEmpty(_coverageIdentifier))
     {
       _logger.LogVerbose($"Setting environment variables for test host");
 
@@ -303,7 +304,7 @@ async Task ITestHostProcessLifetimeHandler.OnTestHostProcessExitedAsync(
     _logger.LogVerbose($"=== OnTestHostProcessExitedAsync START ===");
     _logger.LogVerbose($"Test host PID: {testHostProcessInformation.PID}, ExitCode: {testHostProcessInformation.ExitCode}");
 
-    if (!_coverageEnabled || _coverage == null || _serviceProvider == null)
+    if (!IsCoverageEnabled || _coverage == null || _serviceProvider == null)
     {
       _logger.LogVerbose("Coverage collection skipped (not enabled or not initialized)");
       return;
@@ -332,7 +333,7 @@ async Task ITestHostProcessLifetimeHandler.OnTestHostProcessExitedAsync(
   public Task<bool> IsEnabledAsync()
   {
     DebugHelper.HandleDebuggerAttachment(nameof(CoverletExtension));
-    return Task.FromResult(true);
+    return Task.FromResult(IsCoverageEnabled);
   }
 
   // Add internal setter for testing

src/coverlet.MTP/EnvironmentVariables/CoverletExtensionEnvironmentVariableProvider.cs

@@ -16,6 +16,9 @@ internal sealed class CoverletExtensionEnvironmentVariableProvider : ITestHostEn
 {
   private readonly ILogger _logger;
   private readonly Microsoft.Testing.Platform.CommandLine.ICommandLineOptions _commandLineOptions;
+  private bool? _isCoverageEnabled;
+
+  private bool IsCoverageEnabled => _isCoverageEnabled ??= _commandLineOptions.IsOptionSet(CoverletOptionNames.Coverage);
 
   public CoverletExtensionEnvironmentVariableProvider(
     IConfiguration configuration,
@@ -34,14 +37,16 @@ public CoverletExtensionEnvironmentVariableProvider(
   public string DisplayName => "Coverlet Environment Variable Provider";
   public string Description => "Provides environment variables for Coverlet coverage collection";
 
-  public Task<bool> IsEnabledAsync() => Task.FromResult(true);
+  public Task<bool> IsEnabledAsync()
+  {
+    // Check if --coverlet flag was provided
+    return Task.FromResult(IsCoverageEnabled);
+  }
 
   public Task UpdateAsync(IEnvironmentVariables environmentVariables)
   {
     // Check if --coverlet flag was provided
-    bool coverageEnabled = _commandLineOptions.IsOptionSet(CoverletOptionNames.Coverage);
-
-    if (coverageEnabled)
+    if (IsCoverageEnabled)
     {
       // Tell the test host that coverage is enabled
       environmentVariables.SetVariable(

test/coverlet.MTP.tests/Collector/CollectorExtensionTests.cs

@@ -200,8 +200,24 @@ public void ExtensionPropertyReturnsNonEmptyString(string propertyName)
   #region IsEnabledAsync Tests
 
   [Fact]
-  public async Task IsEnabledAsyncReturnsTrue()
+  public async Task IsEnabledAsyncReturnsFalseIfCoverletOptionNotSet()
   {
+    _mockCommandLineOptions
+      .Setup(x => x.IsOptionSet(CoverletOptionNames.Coverage))
+      .Returns(false);
+    var collector = CreateCollector();
+
+    bool result = await collector.IsEnabledAsync();
+
+    Assert.False(result);
+  }
+
+  [Fact]
+  public async Task IsEnabledAsyncReturnsTrueIfCoverletOptionSet()
+  {
+    _mockCommandLineOptions
+      .Setup(x => x.IsOptionSet(CoverletOptionNames.Coverage))
+      .Returns(true);
     var collector = CreateCollector();
 
     bool result = await collector.IsEnabledAsync();

test/coverlet.MTP.tests/Environment/CoverletExtensionEnvironmentVariableProviderTests.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using coverlet.MTP.EnvironmentVariables;
+using Coverlet.MTP.CommandLine;
 using Coverlet.MTP.Diagnostics;
 using Microsoft.Testing.Platform.CommandLine;
 using Microsoft.Testing.Platform.Configurations;
@@ -68,11 +69,31 @@ public void DescriptionReturnsExpectedValue()
   #region IsEnabledAsync Tests
 
   [Fact]
-  public async Task IsEnabledAsyncReturnsTrue()
+  public async Task IsEnabledAsyncReturnsFalseIfCoverletOptionNotSet()
   {
     // Act
     bool result = await _provider.IsEnabledAsync();
 
+    // Assert
+    Assert.False(result);
+  }
+
+  [Fact]
+  public async Task IsEnabledAsyncReturnsTrueIfCoverletOptionSet()
+  {
+    // Arrange
+    var mockCommandLineOptions = new Mock<ICommandLineOptions>();
+    mockCommandLineOptions.Setup(o => o.IsOptionSet(CoverletOptionNames.Coverage)).Returns(true);
+
+    // Re-create provider to pick up the environment variable
+    var provider = new CoverletExtensionEnvironmentVariableProvider(
+      _mockConfiguration.Object,
+      mockCommandLineOptions.Object,
+      _mockLoggerFactory.Object);
+
+    // Act
+    bool result = await provider.IsEnabledAsync();
+
     // Assert
     Assert.True(result);
   }