Fix dotnet test crash on empty, invalid, or unreadable global.json

[Copilot]

Fix dotnet test command failure when global.json is unreadable

• Understand the codebase and issue
• Add error handling in TestCommandDefinition.Create() for empty/invalid global.json
• Add error handling for File.ReadAllText exceptions (catch all exceptions)
• Add tests for empty, invalid, and unreadable global.json scenarios
• Refactor tests to reduce code duplication
• Run tests to validate the fix (32/32 tests pass)
• Code review completed
• Manual verification completed

Summary

Fixed crashes in dotnet test command when encountering:

1. Empty global.json files
2. Invalid JSON content in global.json
3. Unreadable global.json files (any exception from File.ReadAllText)

All scenarios now default to VSTest, matching the behavior when no global.json exists. Uses broad exception handling for File.ReadAllText to catch all possible file access errors.

Original prompt

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This section details on the original issue you should resolve

<issue_title>dotnet test command definition fails if global.json is unreadable</issue_title>
<issue_description>Create app and add empty global.json. Run dotnet --version.

System.TypeInitializationException: The type initializer for 'Microsoft.DotNet.Cli.Parser' threw an exception.
 ---> System.TypeInitializationException: The type initializer for 'Microsoft.DotNet.Cli.Commands.Test.TestCommandParser' threw an exception.
 ---> System.Text.Json.JsonException: The input does not contain any JSON tokens. Expected the input to start with a valid JSON token, when isFinalBlock is true. Path: $ | LineNumber: 0 | BytePositionInLine: 0.
 ---> System.Text.Json.JsonReaderException: The input does not contain any JSON tokens. Expected the input to start with a valid JSON token, when isFinalBlock is true. LineNumber: 0 | BytePositionInLine: 0.
   at System.Text.Json.ThrowHelper.ThrowJsonReaderException(Utf8JsonReader& json, ExceptionResource resource, Byte nextByte, ReadOnlySpan`1 bytes)
   at System.Text.Json.Utf8JsonReader.Read()
   at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, T& value, JsonSerializerOptions options, ReadStack& state)
   --- End of inner exception stack trace ---
   at System.Text.Json.ThrowHelper.ReThrowWithPath(ReadStack& state, JsonReaderException ex)
   at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, T& value, JsonSerializerOptions options, ReadStack& state)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.Deserialize(Utf8JsonReader& reader, ReadStack& state)
   at System.Text.Json.JsonSerializer.ReadFromSpan[TValue](ReadOnlySpan`1 utf8Json, JsonTypeInfo`1 jsonTypeInfo, Nullable`1 actualByteCount)
   at System.Text.Json.JsonSerializer.ReadFromSpan[TValue](ReadOnlySpan`1 json, JsonTypeInfo`1 jsonTypeInfo)
   at System.Text.Json.JsonSerializer.Deserialize[TValue](String json, JsonSerializerOptions options)
   at Microsoft.DotNet.Cli.Commands.Test.TestCommandDefinition.Create() in E:\sdk2\src\Cli\dotnet\Commands\Test\TestCommandDefinition.cs:line 43
   at Microsoft.DotNet.Cli.Commands.Test.TestCommandParser.CreateCommand() in E:\sdk2\src\Cli\dotnet\Commands\Test\TestCommandParser.cs:line 20
   at Microsoft.DotNet.Cli.Commands.Test.TestCommandParser..cctor() in E:\sdk2\src\Cli\dotnet\Commands\Test\TestCommandParser.cs:line 11
   --- End of inner exception stack trace ---
   at Microsoft.DotNet.Cli.Commands.Test.TestCommandParser.GetCommand() in E:\sdk2\src\Cli\dotnet\Commands\Test\TestCommandParser.cs:line 15
   at Microsoft.DotNet.Cli.Parser..cctor() in E:\sdk2\src\Cli\dotnet\Parser.cs:line 59
   --- End of inner exception stack trace ---
   at Microsoft.DotNet.Cli.Parser.get_RootCommand() in E:\sdk2\src\Cli\dotnet\Parser.cs:line 241
   at Microsoft.DotNet.Cli.Parser.Parse(String[] args) in E:\sdk2\src\Cli\dotnet\Parser.cs:line 253
   at Microsoft.DotNet.Cli.Program.ProcessArgs(String[] args, TimeSpan startupTime) in E:\sdk2\src\Cli\dotnet\Program.cs:line 140
   at Microsoft.DotNet.Cli.Program.Main(String[] args) in E:\sdk2\src\Cli\dotnet\Program.cs:line 89
```</issue_description>

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

<comments>
</comments>

• Fixes dotnet test command definition fails if global.json is unreadable #52384

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[tmat]

@copilot Also handle exception from File.ReadAllText

[tmat]

@copilot Also handle exception from File.ReadAllText

[Copilot]

Added exception handling for File.ReadAllText to catch I/O errors and permission issues. Commit: 400138a

[tmat]

@copilot Catch all extensions here instead of explicit ones.

[Copilot]

Changed to catch all exceptions. Commit: 41f398a