Testing SDK: DiagnosticResult.Message throws System.FormatException

[RikkiGibson]

roslyn-sdk/src/Microsoft.CodeAnalysis.Testing/Microsoft.CodeAnalysis.Analyzer.Testing/DiagnosticResult.cs

Line 63 in 8d0b316

public string Message

This can throw when the diagnostic message has format parameters '{0}', '{1}' etc. This is fine, but maybe the FormatException should be caught and rethrown in a way that's going to make sense/be
more easily actionable to users of the library.

Here's the exception you get:

System.FormatException
  HResult=0x80131537
  Message=Index (zero based) must be greater than or equal to zero and less than the size of the argument list.
  Source=System.Private.CoreLib
  StackTrace:
   at System.Text.StringBuilder.AppendFormatHelper(IFormatProvider provider, String format, ParamsArray args) in E:\A\_work\2188\s\src\mscorlib\shared\System\Text\StringBuilder.cs:line 1743
   at System.String.FormatHelper(IFormatProvider provider, String format, ParamsArray args) in E:\A\_work\2188\s\src\mscorlib\src\System\String.Manipulation.cs:line 513
   at System.String.Format(String format, Object[] args) in E:\A\_work\2188\s\src\mscorlib\src\System\String.Manipulation.cs:line 473
   at Microsoft.CodeAnalysis.Testing.DiagnosticResult.get_Message() in /_/src/Tools/Microsoft.CodeAnalysis.Testing/Microsoft.CodeAnalysis.Analyzer.Testing/DiagnosticResult.cs:line 61

Instead of giving a message like this:

"Index (zero based) must be greater than or equal to zero and less than the size of the argument list"

Let's say something like:

$"{diagnosticResult.ToString()} didn't contain enough arguments for all the format variables in the diagnostic message {diagnosticResult.MessageFormat}."

[sharwell]

This was fixed by @NextTurn in #395