[Test Improver] Add unit tests for ResponseFileHelper.TryReadResponseFile

[Evangelink]

Cover six scenarios: file not found (returns false, adds error with
path), valid file with multiple lines (returns true, tokenizes args),
lines starting with '#' are treated as comments (skipped), blank/
whitespace lines are skipped, quoted arguments are unquoted correctly,
and an empty file returns true with an empty array.

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com

Fixes #8372

[Copilot]

Pull request overview

Adds missing unit test coverage for ResponseFileHelper.TryReadResponseFile, which is used to expand @response-file command-line arguments in Microsoft.Testing.Platform.

Changes:

• Added unit tests covering response-file read behavior for missing files, empty files, multi-line content, comment lines, blank/whitespace lines, and quoted arguments.

Show a summary per file

File	Description
test/UnitTests/Microsoft.Testing.Platform.UnitTests/CommandLine/ResponseFileHelperTests.cs	Adds new TryReadResponseFile unit tests to validate response-file parsing and error reporting behavior.

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 1

[Evangelink]

Good addition of six well-structured TryReadResponseFile tests. All use proper temp-file lifecycle (try/finally + File.Delete), unique paths, and consistent MSTest assertion APIs.

#	Dimension	Verdict
11	Assertion Quality	🟡 2 NIT
13	Test Completeness & Coverage	🟡 1 MODERATE

✅ 19/21 dimensions clean.

Assertion Quality (NIT): Two success-path tests (FileWithComments, FileWithBlankLines) are missing Assert.IsEmpty(errors). The other two success-path tests both include this assertion — the gap is inconsistent and would let a regression that emits spurious errors slip through.

Test Completeness (MODERATE): The IOException branch in TryReadResponseFile (lines 22–24 of ResponseFileHelper.cs) has no test coverage. It produces a different error message (CommandLineParserFailedToReadResponseFile) than the FileNotFoundException branch. Consider adding a test that mocks or creates an unreadable file to exercise this path, or at minimum add a tracking comment/issue.

Generated by Expert Code Review (on open) for issue #8374 · ● 4.8M

[Copilot]

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 1

[Evangelink]

Addressed the MODERATE finding about the uncovered IOException branch: added TryReadResponseFile_FileLocked_ReturnsFalseAndAddsError (commit 906ddf6) which opens the response file with FileShare.None to force File.ReadAllLines to throw IOException and exercises the CommandLineParserFailedToReadResponseFile error path. Gated with [OSCondition(OperatingSystems.Windows)] (per MSTEST0061) because exclusive file locking is only honored on Windows.