BeEquivalentTo incorrectly compare JsonElements?

[Smurfa]

Description

I am trying to compare if two json strings are equivalent (don't care about whitespaces or order). Using suggestion from previous issue: https://github.com/fluentassertions/fluentassertions/issues/1212 yields incorrect results.

Reproduction Steps

[Fact]
public void Test()
{
    var foo = JsonDocument.Parse("""{"test":"something"}""").RootElement;
    var bar = JsonDocument.Parse("""{"test":"something else"}""").RootElement;

    foo.Should().BeEquivalentTo(bar, opt => opt.ComparingByMembers<JsonElement>());
}

Expected behavior

Would expect this to fail, "something" != "something else".

Actual behavior

Test passes.

Regression?

No response

Known Workarounds

No response

Configuration

.NET 7.0 xunit 2.5.0 FluentAssertions 6.12.0

Other information

No response

Are you willing to help with a pull-request?

No

[jnyrup]

My snippet in #1212 only compares the ValueKind property of a JsonElement. The design of JsonElement doesn't let us use the built-in structural equivalency which reflects over the properties on the type. To make it work, you'll have to write a custom IEquivalencyStep.

Here's some code I hacked together in five minutes. It works for your example, but it most likely doesn't work in the general case, so no guarantees are given.

[Fact]
public void Test()
{
    var foo = JsonDocument.Parse("""{"test":"something"}""").RootElement;
    var bar = JsonDocument.Parse("""{"test":"something else"}""").RootElement;

    foo.Should().BeEquivalentTo(bar, opt => opt.Using(new JsonObjectEquivalencyStep()));
}

public class JsonObjectEquivalencyStep : IEquivalencyStep
{
    public EquivalencyResult Handle(Comparands comparands, IEquivalencyValidationContext context, IEquivalencyValidator nestedValidator)
    {
        if (comparands.Subject is not JsonElement subject || comparands.Expectation is not JsonElement expectation)
        {
            return EquivalencyResult.ContinueWithNext;
        }

        if (subject.ValueKind is JsonValueKind.Object && expectation.ValueKind is JsonValueKind.Object)
        {
            var newComparands = new Comparands(subject.EnumerateObject(), expectation.EnumerateObject(), typeof(IEnumerable<JsonProperty>));
            nestedValidator.RecursivelyAssertEquality(newComparands, context);
            return EquivalencyResult.AssertionCompleted;
        }

        if (subject.ValueKind is JsonValueKind.Array && expectation.ValueKind is JsonValueKind.Array)
        {
            var newComparands = new Comparands(subject.EnumerateArray(), expectation.EnumerateArray(), typeof(IEnumerable<JsonElement>));
            nestedValidator.RecursivelyAssertEquality(newComparands, context);
            return EquivalencyResult.AssertionCompleted;
        }

        return EquivalencyResult.ContinueWithNext;
    }
}

Also the failure message is also not as pretty as it could be, as it uses some internal index over the json property name

Expected root[0] to be "test":"something else", but found "test":"something".

[dennisdoomen]

This should also be covered by #2205

[Smurfa]

Sorry for late response and thanks for your replies @jnyrup and @dennisdoomen. Wanted to make sure if I was missing something obvious to make it work out of the box. But then I know it would require some custom comparison implementation to get it working. Cheers!

[dennisdoomen]

@jnyrup what do you think of the PR? It could be a first, rather independent step to proper support for System.Text.Json?

[dennisdoomen]

@jnyrup ?