Add underscore separator support to TestTree

[Copilot]

TestTree only supported dot (.) as a separator for test name hierarchies. Test names using underscores (e.g., Namespace_Class_Method) were not split into proper tree structures.

Changes

• TestTree.cs: Added _ to NameSeparators array and introduced ReconstructPath() to preserve original separators in node paths
• TestTreeTests.cs: Added two test cases verifying underscore-separated names create proper hierarchies and are searchable

Example

var tree = new TestTree();
tree.AddTests(["Namespace_Class_Method"]);

// Creates hierarchy: Namespace -> Class -> Method
var node = tree.FindNodeByPath("Namespace_Class");
// node.FullPath == "Namespace_Class" (preserves original separator)

Mixed separators (Namespace.Class_Method) work as expected, with each separator preserved in the reconstructed path.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Failing Test: Asynkron.TestRunner.Tests.TestTreeTests.AddTests_TestsWithUnderscoreSeparators_SplitsCorrectly</issue_title>
<issue_description>## Failing Test

Test: Asynkron.TestRunner.Tests.TestTreeTests.AddTests_TestsWithUnderscoreSeparators_SplitsCorrectly
Display Name: Asynkron.TestRunner.Tests.TestTreeTests.AddTests_TestsWithUnderscoreSeparators_SplitsCorrectly

Error Message

Expected at least 3 levels, got 1

Stack Trace

   at Xunit.Assert.True(Nullable`1 condition, String userMessage) in /_/src/xunit.assert/Asserts/BooleanAsserts.cs:line 146
   at Xunit.Assert.True(Boolean condition, String userMessage) in /_/src/xunit.assert/Asserts/BooleanAsserts.cs:line 128
   at Asynkron.TestRunner.Tests.TestTreeTests.AddTests_TestsWithUnderscoreSeparators_SplitsCorrectly() in /Users/rogerjohansson/git/asynkron/Asynkron.TestRunner/tests/Asynkron.TestRunner.Tests/TestTreeTests.cs:line 74
   at System.Reflection.MethodBaseInvoker.InterpretedInvoke_Method(Object obj, IntPtr* args)
   at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)

Other Failing Tests in This Run

• Asynkron.TestRunner.Tests.TestTreeTests.FindNodeByPath_WorksWithUnderscoreSeparators

---

Generated by Asynkron.TestRunner at 2026-01-16 11:41:24 UTC
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Failing Test: Asynkron.TestRunner.Tests.TestTreeTests.AddTests_TestsWithUnderscoreSeparators_SplitsCorrectly #11

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.