test.each should perform string interpolation with object properties

[nth-commit]

🚀 Feature Proposal

When giving an array of objects to the test.each overload that accepts an array, and not a template strings table, jest should interpolate the object's properties into the test name.

Motivation

The current interpolation of template strings works great, but it doesn't provide any hook for type-safety. This is problematic when scaling up to large and complex test cases, and in TypeScript, it allows any to sneak into your test functions. It also is more intuitive, it left me wondering for a while why a transformation to a type-safe version of a test wasn't causing interpolation of the test case.

Example

We can do something like this right now:

test.each`
  a    | b    | expectedResult
  ${1} | ${1} | ${2}
  ${2} | ${2} | ${4}
`('add($a, $b) === $expectedResult', ({ a, b, expectedResult }) => {
  expect(a + b).toEqual(expectedResult);
});

Which will output the test cases:
√ add(1, 1) === 2
√ add(2, 2) === 4

In order to achieve type-safety on the same test, I would make this transformation:

type AddExample = {
  a: number;
  b: number;
  expectedResult: number;
};

test.each<AddExample>([
  { a: 1, b: 1, expectedResult: 2 },
  { a: 2, b: 2, expectedResult: 4 },
])('add($a, $b) === $expectedResult', ({ a, b, expectedResult }) => {
  expect(a + b).toEqual(expectedResult);
});

Which I would expect should output the same test cases as above, but instead:
√ add($a, $b) === $expectedResult
√ add($a, $b) === $expectedResult

Pitch

It is isomorphic to functionality in the core library, but I believe it cannot be implemented as an extension.

[SimenB]

@mattphillips thoughts? Seems reasonable to me

[mattphillips]

This has been something I've wanted to add for a while but not got around to it and I think we should add parity with the tagged template table with $ syntax for sure 👍

[nth-commit]

Hey @mattphillips, I was looking at the code to see how I could contribute this change. Was wondering what your thoughts were on ensuring it's not breaking. Perhaps if the test name contains any of the printf special characters, use the printf formatting logic, else use variable interpolation?

[jeysal]

Found this in my inbox and noticed it hasn't been replied to, so I'll just go ahead and answer from my perspective 😅
@nth-commit I would say as long as we land it in a major version (27.0.0 is likely coming up soon), it'd be fine to have the small breaking change. It's particularly small since only existing $variables will be interpolated, $b if there is no b variable in the template string is already being ignored, so most test case names even if they have $ in their name will not be affected.

[github-actions]

This issue has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.
Please note this issue tracker is not a help forum. We recommend using StackOverflow or our discord channel for questions.