Consider CoreChecks.isEquivalentTo

[matanlurey]

In Dart, an object that implements equality in respect to another object is expected to:

• a == b
• a.hashCode == b.hashCode

(It's possible for hashCode's to be equal, but not exact equality, for inequal objects)

To test this feature in my code, I often write a helper like:

extension CoreChecksX<T extends Object?> on Subject<T> {
  /// Expects that this value is equivalent to [other].
  ///
  /// Two objects are considered equivalent if they are equal and have the same
  /// hash code.
  void isEquivalentTo(T other) {
    context.expect(() => prefixFirst('equals ', literal(other)), (actual) {
      if (actual != other) {
        return Rejection(which: ['are not equal']);
      }
      if (actual.hashCode != other.hashCode) {
        return Rejection(which: ['have different hash codes']);
      }
      return null;
    });
  }
}

This often catches subtle bugs where a new field is added, but only == is updated and not hashCode.

Would you consider this in the library itself? I also often introduce hasToString:

/// Returns a subject that expects the [Object.toString] representation of
/// this value.
Subject<String> get hasToString {
  return context.nest<String>(
    () => ['has a string representation'],
    (actual) => Extracted.value(actual.toString()),
    atSameLevel: true,
  );
}

... but happy to consider that separately if you're all interested.