Snapshots not storing function names in Saga objects

[outdooricon]

When I run a test against a Redux Saga Call event, If I want to store the result in a snapshot, the function name being called is important. However, currently when I store it as a snapshot, the function name isn't serialized into the snapshot.

For a test:

describe('Saga', () => {
  const generator = sagaGenerator();
  it('should call fetch command', () => {
    const firstCmd = generator.next().value;
    expect(firstCmd).toEqual(call(fetchCall));
  });
});

Here is what gets put into the snapshot:

exports[`Saga should call fetch command 1`] = `
Object {
  "@@redux-saga/IO": true,
  "CALL": Object {
    "args": Array [],
    "context": null,
    "fn": [Function],
  },
}
`;

However, this is what the test says in the console that it is comparing against when I don't use a snapshot:

Object {
  "@@redux-saga/IO": true,
  "CALL": Object {
    "args": Array [],
    "context": null,
    "fn": [Function fetchCall],
  },
}

Note the Function fetchCall. Without that function name, the snapshot will pass easily for any functions

[thymikee]

I thought it was a bug, but we actually have this behaviour on purpose: https://github.com/facebook/jest/blob/master/packages/jest-snapshot/src/utils.js#L65

@cpojer why would we do that?

[cpojer]

The problem is that function names are not reliable and they also aren't visible in the real user output. It's like testing a private function of a module – if it is important, you should expose it somehow.

Concrete examples where this creates issues:

• node 4 and node 6 have different function name inference
• coverage messes with the function names, so snapshots break when using coverage

See http://facebook.github.io/jest/blog/2016/10/03/jest-16.html#snapshot-updates

[outdooricon]

Thank you Christoph! Is there another way to test Saga call actions then, using snapshot, or do you just recommend not using it for those?

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