Jest's it.each method is throwing an error: "This expression is not callable. Type 'String' has no call signatures."

I've been attempting to utilize the describe.eachtable feature with TypeScript, but I keep running into an error message stating: "error TS2349: This expression is not callable. Type 'String' has no call signatures."

Below is my code snippet:

  it.each(
    `field       |      expectedMessage
    ${"username"} | ${"Username cannot be null"}
  `(
      "returns $expectedMessage when $field is null",
      async ({ field, expectedMessage }) => {
           ...
       )
  );

In Visual Studio Code (VSCode), the error appears like this:

https://i.stack.imgur.com/3egy3.png I'm unsure how to resolve this typing issue because the syntax seems a bit unfamiliar to me.

I attempted to type it based on the guidance from the documentation as follows:

it.each(<{field: string; expectedMessage: string}>
    `field       |      expectedMessage
    ${"username"} | ${"Username cannot be null"}
  `(

However, the situation only deteriorated:

https://i.stack.imgur.com/4ZewD.png

Answer №1

You made a mistake, please correct it

it.each`
    field         | expectedMessage
    ${'email'} | ${'Email must be valid'}
`('displays $expectedMessage when $field is not valid', async ({ field, expectedMessage }) => {
    // ..
    console.log(field, expectedMessage);
    expect(2 + 2).toBe(4);
});

Alternatively, provide specific parameters to test.each explicitly:

import { test } from '@jest/globals';

test.each<{ field: string; expectedMessage: string }>`
    field         | expectedMessage
    ${'password'} | ${'Password must contain at least 8 characters'}
`('example using template literals', ({ field, expectedMessage }) => {
    // if generic argument is omitted, types default to `unknown`
});

current version of packages used:

"@types/jest": "^30.0.1",
"jest": "^30.1.0",
"ts-jest": "^30.1.2",
"typescript": "^5.3.0"

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