A test said the server started. I deleted the server. It still passed.

Here is a test from a real, well run Node project: test ( ' server starts ' , async ( t ) => { const app = build () await app . listen ({ port : 0 }) t . assert . ok ( true , ' server started ' ) }) It reads fine in review. It runs green. Now delete the body of build() so the server never comes up. The test is still green, because the only thing it asserts is true . In the same file two more of these caught the error in a catch and asserted true there too, so even the failure path was green. That is not a made up example. I found it in fastify at a pinned commit and opened a PR to fix it. More on that at the end. A whole class of tests cannot fail Once you start looking, the pattern turns up in a few shapes: A literal: assert.ok(true) , expect(1).toBe(1) , a snapshot of a constant. An assertion parked in a catch the happy path never reaches, so nothing is checked when the code works and nothing is checked when it breaks. A status list that accepts both outcomes: assert.ok([200, 500].includes(res.status)) . Each one runs, counts toward coverage and guards nothing. Coverage is the trap. The line executed, so the tool that counts executed lines is happy. Whether the line would go red on a regression is a different question. It is the one that matters. Why review misses it A reviewer reading the diff sees a test called server starts , an await listen and a green tick. The name states intent. The assertion is what actually runs, yet ok(true) does not look like a problem until you stop and ask what would ever turn this test red. A missing check does not show up in a diff the way a wrong line does. Finding them I wrote a small scanner for this. No account, no config file, no network call: npx margyn-scan /path/to/repo One of its checks is cannot-fail : tests whose assertions hold whatever the code does. It also flags tests that assert nothing at all, files the build reads that git never committed, gates declared in package.json that no workflow invokes and linter exclusion