editorconfig rule to enforce that namespace is set in all C# files

Based on the comment from Jon Skeet that this probably is not possible with editorconfig, I wrote a generic unit test for it.

using System.Text.RegularExpressions;
using Shouldly;

namespace Base.SharedTests.UnitTests;

public partial class CodeTests
{
    [Fact]
    public void AllFiles_WithCsExtension_ShouldHaveFileScopedNamespaces()
    {
        var solutionBasePath = Path.GetFullPath(
            Path.Combine(AppContext.BaseDirectory, "..", "..", "..", "..", "..")
        );

        var files = Directory
            .GetFiles(solutionBasePath, "*.cs", SearchOption.AllDirectories)
            .Where(f => !f.EndsWith("GlobalUsings.cs", StringComparison.Ordinal))
            .Where(f => !f.EndsWith("Program.cs", StringComparison.Ordinal))
            .Where(f => !f.Contains("/bin/", StringComparison.Ordinal))
            .Where(f => !f.Contains("/obj/", StringComparison.Ordinal));

        List<(string FileName, bool Result)> results =
        [
            .. files.Select(f =>
            {
                var text = File.ReadAllText(f);
                var fileName = Path.GetFileName(f);
                var result = NamespaceRegex().IsMatch(text);

                return (fileName, result);
            }),
        ];

        results.ShouldAllBe(r => r.Result == true);
    }

    [GeneratedRegex(@"^\s*namespace\s+[A-Za-z0-9_.]+\s*;", RegexOptions.Multiline)]
    private static partial Regex NamespaceRegex();
}