Add proper rule tests

[sindresorhus]

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[chatgpt-codex-connector]

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[som-sm]

@sindresorhus Apologies for the delay on this, I'm a bit occupied with some household work. But, I'll get to this sometime this week or next.

[sindresorhus]

@som-sm Would be good to get this merged so it can also be used in your #1265 PR.

[som-sm]

@som-sm Would be good to get this merged so it can also be used in your #1265 PR.

Yeah, yeah, I had some thoughts around this. Give me a couple of days, and I'll give this a proper read and get back.

[som-sm]

@sindresorhus QQ, out of curiosity, is the code on these on-disk files actually being used anywhere?

From my initial testing:

Create source/exported-type.d.ts file with some arbitrary content:

const {ruleTester, fixturePath} = createTypeAwareRuleTester({
	'package.json': `${packageContent}\n`,
	'index.d.ts': indexContent,
	'source/exported-type.d.ts': 'The code here isn\'t being used anywhere, because the virtual file will overwrite it.',
	// ...
});

The code that we specify in code is what is being used for linting:

const exportedTypeContent = 'export type ExportedType = {\n\tvalue: string;\n};\n';

ruleTester.run('require-exported-types', requireExportedTypesRule, {
	valid: [
		{
			code: exportedTypeContent,
			filename: fixturePath('source/exported-type.d.ts'),
		},
	],
	invalid: [],
});

Verified this using the following log in the lint rule:

console.log({
    sourceCode: context.sourceCode.text,
});

This log prints:

{ sourceCode: 'export type ExportedType = {\n\tvalue: string;\n};\n' }

Creating index.d.ts and package.json files on disk makes sense because the individual test cases don't create those files. But having to create files on disk for all test cases beforehand feels odd to me, but maybe that's a standard practice.

Does it make sense to set them to undefined instead?

const {ruleTester, fixturePath} = createTypeAwareRuleTester({
	'package.json': `${packageContent}\n`,
	'index.d.ts': indexContent,
	'source/exported-type.d.ts': undefined,
	'source/internal/internal-type.d.ts': undefined,
	'source/internal/nested/deep.d.ts': undefined,
	'source/private-type.d.ts': undefined,
	'source/missing-type.d.ts': undefined,
	'source/unexported-multiple.d.ts': undefined,
	'source/implementation.ts': undefined,
	'test/test.d.ts': undefined,
	'lib/test.d.ts': undefined,
});

And, in test-utils.js add an empty string fallback:

fs.writeFileSync(absolutePath, content ?? '');

[som-sm]

IMO, it would have been better if we had to create only the files that are separate from the ones we're linting, i.e., index.d.ts and package.json.

But it seems like doing that brings in a lot of other complications. Here's all I had to do to get it working:

import {createTypeAwareRuleTester} from './test-utils.js';
import {requireExportedTypesRule} from './require-exported-types.js';

const packageContent = JSON.stringify({
	name: 'require-exported-types-fixture',
}, null, '\t');
const indexContent = 'export {type ExportedType} from \'./source/exported-type\';\n';
const exportedTypeContent = 'export type ExportedType = {\n\tvalue: string;\n};\n';

const {ruleTester, fixturePath} = createTypeAwareRuleTester({
	'package.json': `${packageContent}\n`,
	'index.d.ts': indexContent,
}, {
	ruleTester: {
		languageOptions: {
			parserOptions: {
				projectService: {
					allowDefaultProject: ['source/*.ts*'],
				},
			},
		},
	},
});

const withIndexReference = code => `/// <reference path="${fixturePath('index.d.ts')}" />\n${code}`;

ruleTester.run('require-exported-types', requireExportedTypesRule, {
	valid: [
		{
			code: withIndexReference(exportedTypeContent),
			filename: fixturePath('source/exported-type.d.ts'),
		},
	],
	invalid: [],
});

Changes:

1. Only index.d.ts and package.json files are being created on disk.
2. Had to update allowDefaultProject to include 'source/exported-type.d.ts'.
3. Had to add /// <reference path="${fixturePath('index.d.ts')}" /> in code to include index.d.ts, otherwise index.d.ts seems to not be part of the program.

[sindresorhus]

Does it make sense to set them to undefined instead?

Makes sense. Done.

[som-sm]

PR LGTM, just few comments regarding adding some test cases.