MC/DC coverage for JavaScript
A checkout function can have 100% line and branch coverage without a test for an expired session. Both return paths run. Both tests pass. But removing the expiry check still leaves the suite green. MC/DC coverage asks a more specific question: has each condition been shown to change the decision on its own? Here's what that looks like in JavaScript, using a small example we ran with Supercov. The…
JavaScript code coverage tools can measure Modified Condition/Decision Coverage (MC/DC), which ensures each condition independently affects the decision outcome. In this example, a checkout function's condition is signedIn && !expired. To achieve MC/DC, tests must demonstrate that changing one condition independently alters the decision's result.
The original tests cover valid sessions and signed-out users but miss the case where a signed-in customer has an expired session. To address this gap, a new test is added to check the checkout denial for a signed-in customer with an expired session. After adding this test, MC/DC coverage improves to 50%, indicating the condition now independently affects the decision outcome.
Written by urgent.news from Dev.to's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
