Using fluture/test/assertions.js with Json is never reference-equal

[dotnetCarpenter]

Using fluture/test/assertions.js with Json is never reference-equal when Json is imported from a commonjs module and esm module and compared with equivalence.

When using Json from 'fluture-express', if you test subject is a commonjs module, then the value in the Json object is not reference-equal and tests with equivalence from 'fluture/test/assertions.js' will fail even though the tests should pass.

Error:
	resolve ({"body": {"data": {"foo": "bar"}}, "head": []}) :: Future({ <resolved> {"body": {"data": {"foo": "bar"}}, "head": []} })
is not equivalent to:
	resolve ({"body": {"data": {"foo": "bar"}}, "head": []}) :: Future({ <resolved> {"body": {"data": {"foo": "bar"}}, "head": []} })

The inner values are not equal: Values have same structure but are not reference-equal

Example of error message when Json is not imported via esm.

However, note that it does not matter if your test data is from a commonjs module or EcmaScript module (esm).

A thorough run down is in the https://github.com/dotnetCarpenter/fluture-test-gotcha repository.

It boils down to strictEqual and show from 'sanctuary-show' not playing nice together. I guess that the output of show (a) changes depending on module format. But that is a guess.

// always success
deepStrictEqual (Json (data1), Json (data1));
deepStrictEqual (Json (data2), Json (data2));
// always failure
strictEqual (Json (data1), Json (data1));
strictEqual (Json (data2), Json (data2));

strictEqual.mjs and strictEqual.js

[dotnetCarpenter]

equivalence checks the inner value of two Futures using assert.deepStrictEqual.
That in turn test the prototypes of the inner value.
Because Json has a CommonJS version and a ESM version, those two prototypes
will be different and equivalence will fail for two seemingly identical values.

[Avaq]

We are working on a solution, which is twofold:

1. Fix some issues with value equality #32
2. Update the equals function to fall back to structural equality sanctuary-js/sanctuary-type-classes#154

Once those have both landed, I will update the default equivalence function to use the new Z.equals instead.

Until then, you can use makeEquivalence with a custom equality assertion that wouldn't treat these objects as differently. Perhaps this will do:

const equivalence = makeEquivalence (a => b => {
  if (Z.equals (a, b) || util.isDeepStrictEqual (a, b)) return;
  throw new AssertionError (...)
})

[dotnetCarpenter]

Thanks! I will try it out