Test Runner: In-source testing

[nickserv]

What is the problem this feature will solve?

In-source tests let you write some tests in the same files as their implementation.

Vitest's explanation:

This makes the tests share the same closure as the implementations and able to test against private states without exporting. Meanwhile, it also brings a closer feedback loop for development.

Building this into Node would also have the advantage of letting tutorials and examples for Node users show tests in the same files.

What is the feature you are proposing to solve the problem?

A --test-source flag that will run any Node files and expose the test function via import.meta.test (as importing it could cause it to be accidentally bundled).

if (import.meta.test) {
  import.meta.test("Array.indexOf()", () => {
    assert.strictEqual([1, 2, 3].indexOf(4), -1)
  })
}

The rest of the node:test module could also be exposed as properties of the import.meta.test function.

if (import.meta.test) {
  const { describe, it } = import.meta.test
  describe("Array", () => {
    describe("#indexOf()", () => {
      it("should return -1 when the value is not present", () => {
        assert.strictEqual([1, 2, 3].indexOf(4), -1)
      })
    })
  })
}

What alternatives have you considered?

• Vitest
• Rust

[MoLow]

import.meta is an ESM thing, so if we decide to add this feature we can probably make it with an API that will work for both CJS and ESM:

const {inlineTest, describe, it} = require('node:test');
if (inlineTest) {
  describe("Array", () => {
    describe("#indexOf()", () => {
      it("should return -1 when the value is not present", () => {
        assert.strictEqual([1, 2, 3].indexOf(4), -1)
      })
    })
  })
}

[nickserv]

This would import the whole module, though. I was trying to avoid that, and it's the reason Vitest has a similar API (though it's ESM only). Perhaps we could use properties on require or module for CJS?

[debadree25]

So if I understand correctly if we ran node --test some-file-with-inline-test.mjs then the test module would get included in the import meta and the test suites should be run?

[MoLow]

I am closing as wont do, feel free to reopen if you intend to work on this

[nickserv]

So you'd consider merging a prototype? I can give it a try if we can reach consensus on an import syntax, though it's be easier to discuss this if you could reopen the issue.

[cjihrig]

@nickmccurdy do you have any update on this? If not, I propose closing the issue. That wouldn't stop you from working on it if you really want to see this happen.

[cjihrig]

No follow up for two weeks. Closing.