Update coverage format option handling and exit code mapping

- Allow multiple --formats options (ArgumentArity.OneOrMore) instead of comma-separated values
- Enforce single, supported format per --formats argument
- Update tests to use repeated --formats options
- Expand and clarify process exit code to error message mapping

Author: Bertk

src/coverlet.MTP/CommandLine/CoverletCommandLineOptionsProvider.cs

@@ -51,7 +51,7 @@ public IReadOnlyCollection<CommandLineOption> GetCommandLineOptions()
 
       new(FormatsOptionName,
           "Output format(s) for coverage report (json, lcov, opencover, cobertura). Multiple formats can be specified comma-separated.",
-          ArgumentArity.ExactlyOne, isHidden: false),
+          ArgumentArity.OneOrMore, isHidden: false),
 
       //new(OutputOptionName,
       //    "Output path for coverage files",

src/coverlet.MTP/CoverletExtensionCommandLineProvider.cs

@@ -55,6 +55,7 @@ public Task<ValidationResult> ValidateOptionArgumentsAsync(CommandLineOption com
 
       foreach (string format in arguments)
       {
+        // does not support string with multiple formats e.g. "json,lcov"
         if (!s_supportedFormats.Contains(format))
         {
           return Task.FromResult(ValidationResult.Invalid($"The value '{format}' is not a valid option for '{commandOption.Name}'."));

test/coverlet.MTP.validation.tests/CollectCoverageTests.cs

@@ -198,7 +198,7 @@ public async Task MultipleCoverageFormats_GeneratesAllReports()
     // Act
     var result = await RunTestsWithCoverage(
       testProject.ProjectPath,
-      "--coverlet-coverage --formats json,cobertura,lcov",
+      "--coverlet-coverage --formats json --formats cobertura --formats lcov",
       testName: TestContext.Current.TestCase!.TestMethodName!);
 
     TestContext.Current?.AddAttachment("Test Output", result.CombinedOutput);
@@ -544,13 +544,21 @@ private async Task<TestResult> RunTestsWithCoverage(string projectPath, string a
 
     string errorContext = process.ExitCode switch
     {
-      0 => "Success",
-      1 => "Test failures occurred",
-      2 => "Invalid command-line arguments",
-      3 => "Test discovery failed",
-      4 => "Test execution failed",
-      5 => "Unexpected error (unhandled exception)",
-      _ => "Unknown error"
+      0 => "Success, no errors",
+      1 => "unknown errors",
+      2 => "test failure",
+      3 => "test session was aborted",
+      4 => "setup of used extensions is invalid",
+      5 => "command line arguments passed to the test app are invalid",
+      6 => "test session is using a non-implemented feature",
+      7 => "unable to complete successfully (likely crashed)",
+      8 => "test session ran zero tests",
+      9 => "minimum execution policy for the executed tests was violated",
+      10 => "test adapter, Testing.Platform Test Framework, MSTest, NUnit, or xUnit, failed to run tests for an infrastructure reason",
+      11 => "test process will exit if dependent process exits",
+      12 => "test session was unable to run because the client does not support any of the supported protocol versions",
+      13 => "excited number of maximum failed tests ",
+      _  => "unrecognized exit code"
     };
 
     return new TestResult