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test: resolve flakiness in --mcp flag test #19993

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Merged
merged 1 commit into from
Aug 8, 2025
+6 −2
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test: resolve flakiness in --mcp flag test #19993

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8 changes: 6 additions & 2 deletions tests/bin/eslint.js
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Original file line number Diff line number Diff line change
Expand Up @@ -1343,15 +1343,19 @@ describe("bin/eslint.js", () => {
describe("MCP server", () => {
it("should start the MCP server when the --mcp flag is used", done => {
const child = runESLint(["--mcp"]);
let doneCalled = false;

// should not have anything on std out
child.stdout.on("data", data => {
assert.fail(`Unexpected stdout data: ${data}`);
});

child.stderr.on("data", data => {
assert.match(data.toString(), /@eslint\/mcp/u);
done();
if (!doneCalled) {
assert.match(data.toString(), /@eslint\/mcp/u);
doneCalled = true;
done();
}
Comment on lines 1348 to +1358
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Can we just use getOutput here to test both the error message and the (lack of) stdout output, as it's done in other tests?

eslint/tests/bin/eslint.js

Lines 1219 to 1224 in 8662ed1

const outputAssertion = getOutput(child).then(output => {
const expectedSubstring = "Syntax error in selector";
assert.strictEqual(output.stdout, "");
assert.include(output.stderr, expectedSubstring);
});

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I did use getOutput first, but the test fails with the error:

Error: Timeout of 10000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves.

I think it's because the MCP server process isn't exiting on its own, so getOutput never resolves.

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Ah, of course. Then let's go ahead and merge this change. It looks like this resolves situations like https://github.com/eslint/eslint/actions/runs/16801498351/job/47583769079, where the server manages to print its initial debug message to stderr before the process is terminated.

});
});
});
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