Add Tell Jest To Focus On Running Only One Test as a JavaScript TIL

javascript/tell-jest-to-focus-on-running-only-one-test.md

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+# Tell Jest To Focus On Running Only One Test
+
+Test output can be noisy. Sometimes one test is inadvertently dependent on
+another. These are some of the reasons you may want to tell
+[Jest](https://jestjs.io/) to focus in and only run one particular `test`
+block.
+
+You can do this by calling
+[`test.only()`](https://jestjs.io/docs/setup-teardown#general-advice) instead
+of `test()`.
+
+Find the test block you are interested in focusing on and update it to look
+like this:
+
+```javascript
+// tests above ...
+
+test.only('ensure the function returns the value', () => {
+  // ...
+  // test implementation
+  // ...
+})
+
+// tests below ...
+```
+
+With that 5-character addition (`.only`) we instruct Jest to run that one test
+while skipping all others.
+
+This is particularly useful when you are doing some `console.log` debugging of
+a test. You can eliminate any confusion about which test is logging out by only
+running one test.
+
+[source](https://stackoverflow.com/a/42828586/535590)