fix: prevent flaky tests by disabling parallel execution for registry tests (#584)

Tests using CommandMetadataRegistry share static state and were failing
intermittently when run in parallel. Added [Collection("MetadataRegistry")]
attribute to all test classes that interact with the registry to ensure
they run sequentially.

Affected test classes:
- CommandMetadataRegistryTests
- ConventionAotPathTests
- MetadataProviderTests
- RemainingArgsPropertyConventionTests

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: natemcmaster

test/CommandLineUtils.Tests/RemainingArgsPropertyConventionTests.cs

@@ -10,6 +10,8 @@
 
 namespace McMaster.Extensions.CommandLineUtils.Tests
 {
+    // Uses shared static CommandMetadataRegistry - must not run in parallel with other registry tests
+    [Collection("MetadataRegistry")]
     public class RemainingArgsPropertyConventionTests : ConventionTestBase
     {
         public RemainingArgsPropertyConventionTests(ITestOutputHelper output) : base(output)

test/CommandLineUtils.Tests/SourceGeneration/CommandMetadataRegistryTests.cs

@@ -8,6 +8,8 @@
 
 namespace McMaster.Extensions.CommandLineUtils.Tests.SourceGeneration
 {
+    // Uses shared static CommandMetadataRegistry - must not run in parallel with other registry tests
+    [Collection("MetadataRegistry")]
     public class CommandMetadataRegistryTests
     {
         [Command(Name = "test1")]

test/CommandLineUtils.Tests/SourceGeneration/ConventionAotPathTests.cs

@@ -14,6 +14,8 @@ namespace McMaster.Extensions.CommandLineUtils.Tests.SourceGeneration
     /// Tests for the AOT-friendly code paths in conventions.
     /// These tests exercise the generated metadata paths in conventions.
     /// </summary>
+    // Uses shared static CommandMetadataRegistry - must not run in parallel with other registry tests
+    [Collection("MetadataRegistry")]
     public class ConventionAotPathTests : IDisposable
     {
         public ConventionAotPathTests()

test/CommandLineUtils.Tests/SourceGeneration/MetadataProviderTests.cs

@@ -8,6 +8,8 @@
 
 namespace McMaster.Extensions.CommandLineUtils.Tests.SourceGeneration
 {
+    // Uses shared static CommandMetadataRegistry - must not run in parallel with other registry tests
+    [Collection("MetadataRegistry")]
     public class MetadataProviderTests
     {
         [Command(Name = "test", Description = "A test command")]