Confusing error on missing toMatchSnapshot() argument

[gaearon]

🐛 Bug Report

When toMatchSnapshot(propertyMatchers, snapshotName) has null as the first argument, Jest prints a confusing error:

  Received value does not match snapshot properties for "foo: hello 1".

    Expected snapshot to match properties:
      null
    Received:
      "foo"

To Reproduce

Steps to reproduce the behavior:

it('foo', () =>
  expect('foo').toMatchSnapshot(null, 'hello')
);

with Jest 23

Expected behavior

I only wanted to specify snapshotName. The docs say it's the second argument: http://jestjs.io/docs/en/expect.html#tomatchsnapshotpropertymatchers-snapshotname

I have no idea what "property matchers" are and am not currently interested in them. (The docs fail to mention their format.) I passed null because I don't know what their default value is (the docs fail to mention that too).

I couldn't figure out for quite some time why my tests were failing. I expected null to be treated as a "missing" value for propertyMatchers instead of trying to treat it as some kind of a shape.

Link to repl or repo (highly encouraged)

Repl seems to be on an older Jest version without this problem.

But the above repro works for a clear Jest 23 install.

[gaearon]

The most confusing part of this experience was Jest telling me to re-run my snapshots with -u to record changes, but -u not doing anything. I wasted some time digging why -u wasn't being passed to CLI (which it actually was).

[SimenB]

You can do expect('foo').toMatchSnapshot('hello'). That should definitely be in the docs. Wanna send a PR for it?

@rickhanlonii we should improve the error message here

[rickhanlonii]

fwiw the docs say that the property matchers are optional

I added a better error message here: #6528

[github-actions]

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