unexpected output when using custom toJSON

🐛 Bug Report

I got the following report from Jest:

  ● should work

    expect(received).toEqual(expected)

    Expected: "Hello World"
    Received: "Hello World"

This is very confusing as both texts are exactly the same.

To Reproduce

class MyComponent {
  toJSON() {
    return "Hello World";
  }
}

it("should work", () => {
  const comp = new MyComponent();
  expect(comp.toJSON()).toEqual("Hello World") // <-- this works
  expect(comp).toEqual("Hello World") // <-- this doesn't work
});

Expected behavior

I should work the same way as the previous assertion OR if this is expected behavior, the output message should explain what’s wrong.

Link to repl or repo (highly encouraged)

https://repl.it/repls/TurboGlassMotion

Run npx envinfo --preset jest

Paste the results here:

  System:
    OS: macOS 10.14.3
    CPU: (4) x64 Intel(R) Core(TM) i5-6500 CPU @ 3.20GHz
  Binaries:
    Node: 10.15.2 - /usr/local/bin/node
    npm: 6.4.1 - /usr/local/bin/npm
  npmPackages:
    jest: 24.3.1 => 24.3.1 

[pedrottimark]

Yes:

• @SimenB I think when we responded to request not to display diff for one-line strings, we temporarily lost the no visual difference message.
• @jeysal Good point, it is another example for data-driven diff.

@goenning The “this doesn’t work” assertion compares an object to a string, which fails, and then the custom serialization makes it looks as if it should have passed. So that I can understand the context, did you decide that the “this works” assertion is what you meant to test?

[github-actions[bot]]

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