Custom asymmetric expect matchers aren't able to print Symbol arguments in error reports.

[Ross-Esmond]

🐛 Bug Report

If a symbol is used as an argument to an asymmetric matcher expect will fail when it tries to .join(', ') the arguments while printing the error report.

To Reproduce

There's no reason to want to do this specifically, but it does reproduce the issue.

expect.extend({
  toBeSymbol (received, symbol) {
    return {
      pass: received === symbol,
      message: () => ''
    }
  }
})

test('should throw', function () {
  const foo = Symbol('foo')
  const bar = Symbol('bar')

  expect({ a: foo }).toEqual({
    a: expect.toBeSymbol(bar)
  })
})

Expected behavior

Jest should be able to produce a clean diff which identifies the asymmetric matcher as: toBeSymbol<Symbol(bar)> but instead the expect package fails to build a diff and errors out with TypeError: Cannot convert a Symbol value to a string

Link to repl

repl.it demo Repl's standard Jest is version 22 so I had to import expect directly. Still isolates the issue.

I'll have a pull request soon. Even if it's not merged it'll still show exactly what the issue is. Having trouble building. Might have to postpone this. Apparently .join('') doesn't implicitly convert values to strings. So this line is failing when given a Symbol argument. maping the array toStrings fixes it.

[github-actions]

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