Description

BeEquivalentTo reports an incorrect message when dictionaries have same number of items and first items match, but some item has key mismatch. The message says that the key is missing from pair[key] where key is the first item key value. It's hard to describe, so see fiddle and example below.

See fiddle https://dotnetfiddle.net/DeeDi2

Complete minimal example reproducing the issue

var actual = new Dictionary<string,string>
{
	{"a", "x"},
	{"b", "x"},
};
var expected = new Dictionary<string,string>
{
	{"a", "x"},
	{"c", "x"}, // key mismatch
};

actual.Should().BeEquivalentTo(expected);

Expected behavior:

Logged output should be something like: Expected subject to contain key "c".

If remove the item with key "a" from both actual and expected, then output references subject, correctly.

Actual behavior:

Logged output: Expected pair[a] to contain key "c".

Versions

• Which version of Fluent Assertions are you using? Tried with latest: 6.0.0.0-alpha0001, as well as 5.10.3. Same results in both.
• Which .NET runtime and version are you targeting? .NET Core 3.1.

Additional Information

I discovered this issue at same time: #1449