Description
Currently, the following code doesn't produce any errors neither from TS, nor from @typescript/eslint and eslint-plugin-jest:
const getNames = (): string[] => {
return ['one', 'two'];
};
test('...', () => {
const names = getNames();
expect(names).toBeDefined();
});Note the string[] return type of getNames() function. It's literally always "defined" so .toBeDefined() does not make any sense here, but neither TS nor ESLint complain about it, giving developers a false feeling of good tests.
Actual result: no errors, tests obviously pass while they make no sense.
Expected result: linter error saying Type of "app" variable is "TestingModule", it can not be undefined. It is useless to check it with .toBeDefined() matcher.
Example:
Do you think eslint-plugin-jest is the right place to have a new rule, checking already known types of variables and checking matchers, disallowing useless usage?
Some expiration for implementation can be found in typescript-eslint's no-unnecessary-type-assertion