Inline snapshots?

[lydell]

Jest has inline snapshots. I quite like them for testing strings, such as error messages and CLI output.

• I can just write expect(errorMessage).toMatchInlineSnapshot(). No fiddly copy-pasting and manual typing of the expected value.
• Jest automatically fills in the actual value inside the ().
• I look at the filled in value if it looks ok.
• If I ever tweak that error message, I can just tell Jest to update the snapshot.
• I get to see both the test code and the expected output in one place (don’t need to jump to a separate snapshot file).
• Inline snapshots feels a lot like testing your code by running stuff in the REPL and looking at the results (easy and fast), with the big bonus that you can re-run all tests later!

Here’s an example from a project I’m working on:

    test("empty outputs", async () => {
      expect(await run("elm-tooling-json-decode-error/empty-outputs", ["make"]))
        .toMatchInlineSnapshot(`
        ⧙-- INVALID elm-tooling.json FORMAT ---------------------------------------------⧘
        /Users/you/project/tests/fixtures/errors/elm-tooling-json-decode-error/empty-outputs/elm-tooling.json

        I read inputs, outputs and options from ⧙elm-tooling.json⧘.

        ⧙I had trouble with the JSON inside:⧘

        At root["x-elm-watch"]["outputs"]:
        Expected a non-empty object
        Got: {}
      `);
    });

Has anything like this ever been discussed in AVA? I tried to search but couldn’t find anything. Is this something there would be interest in?

I like this feature of Jest very much, but I also like the leanness of AVA!

Two random references (not sure if they help at all):

• Jest’s code (jest-snapshot package): https://github.com/facebook/jest/tree/master/packages/jest-snapshot
• An assertion library implementing inline snapshots (haven’t tried it): https://github.com/unexpectedjs/unexpected-snapshot

[novemberborn]

AVA's snapshots are not text based, so I think this would become quite awkward. We'd have to put an additional base64-encoded segment in there.