C# source code comparison / assertion helper (depends on the packages Microsoft.CodeAnalysis.CSharp and DiffPlex).

StringAssertionExtensions.cs

using System;
using System.Text;
using DiffPlex.DiffBuilder;
using DiffPlex.DiffBuilder.Model;
using FluentAssertions.Execution;
using FluentAssertions.Primitives;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;

namespace FluentAssertions
{
	public static class StringAssertionExtensions
	{
		public static AndConstraint<StringAssertions> HaveEquivalentSyntaxTreeTo(this StringAssertions assertions, string expectedCode)
		{
			var subject = CSharpSyntaxTree.ParseText(assertions.Subject);
			var expected = CSharpSyntaxTree.ParseText(expectedCode);

			Execute.Assertion
				.ForCondition(subject.IsEquivalentTo(expected, topLevel: false))
				.FailWith(() =>
				{
					var formattedSubject = subject.GetRoot().NormalizeWhitespace(eol: Environment.NewLine).GetText().ToString();
					var formattedExpected = expected.GetRoot().NormalizeWhitespace(eol: Environment.NewLine).GetText().ToString();

					var msgBuilder = new StringBuilder();
					msgBuilder.AppendLine("Expected the syntax tree for: ");
					msgBuilder.AppendLine();
					msgBuilder.Append("  ");
					msgBuilder.AppendLine(formattedSubject.Replace(Environment.NewLine, $"{Environment.NewLine}  ", StringComparison.Ordinal));
					msgBuilder.AppendLine();
					msgBuilder.AppendLine("To be equivalent to the syntax tree for: ");
					msgBuilder.AppendLine();
					msgBuilder.Append("  ");
					msgBuilder.AppendLine(formattedExpected.Replace(Environment.NewLine, $"{Environment.NewLine}  ", StringComparison.Ordinal));
					msgBuilder.AppendLine();
					msgBuilder.AppendLine("The diff between the two is:");
					msgBuilder.AppendLine();

					var diff = InlineDiffBuilder.Diff(formattedExpected, formattedSubject, ignoreWhiteSpace: true);

					foreach (var line in diff.Lines)
					{
						switch (line.Type)
						{
							case ChangeType.Inserted:
								msgBuilder.Append("+ ");
								break;
							case ChangeType.Deleted:
								msgBuilder.Append("- ");
								break;
							default:
								msgBuilder.Append("  ");
								break;
						}

						msgBuilder.AppendLine(line.Text);
					}

					var msg = msgBuilder.Replace("{", "{{").Replace("}", "}}").ToString();
					return new FailReason(msg);
				});

			return new AndConstraint<StringAssertions>(assertions);
		}
	}
}

This allows you to do:

var actualCode = "... some c# code";
var expectedCode=  "... some c# code";

actualCode.Should().HaveEquivalentSyntaxTreeTo(expectedCode);