mozilla-central/devtools/docs/contributor/tests/writing-perf-tests-example.md

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# Performance test example: performance of click event in the inspector
Let's look at a trivial but practical example and add a simple test to measure the performance of a click in the inspector.
First we create a file under [tests/inspector](https://searchfox.org/mozilla-central/source/testing/talos/talos/tests/devtools/addon/content/tests/inspector) since we are writing an inspector test. We call the file `click.js`.
We will use a dummy test document here: `data:text/html,click test document`.
We prepare the imports needed to write the test, from head.js and inspector-helper.js:
- `testSetup`, `testTeardown`, `openToolbox` and `runTest` from head.js
- `reloadInspectorAndLog` from inspector-helper.js
The full code for the test looks as follows:
```
const {
reloadInspectorAndLog,
} = require("devtools/docs/tests/inspector-helpers");
const {
openToolbox,
runTest,
testSetup,
testTeardown,
} = require("devtools/docs/head");
module.exports = async function() {
// Define here your custom document via a data URI:
const url = "data:text/html,click test document";
await testSetup(url);
const toolbox = await openToolbox("inspector");
const inspector = toolbox.getPanel("inspector");
const window = inspector.panelWin; // Get inspector's panel window object
const body = window.document.body;
await new Promise(resolve => {
const test = runTest("inspector.click");
body.addEventListener("click", function () {
test.done();
resolve();
}, { once: true });
body.click();
});
// Check if the inspector reload is impacted by click
await reloadInspectorAndLog("click", toolbox);
await testTeardown();
}
```
```
{
name: "inspector.click",
path: "inspector/click.js",
description:
"Measure the time to click in the inspector, and reload the inspector",
},
```
Since this is an inspector test, we add it under `TEST_SUITES.INSPECTOR`, which contains all the tests which will run with the `damp-inspector` test suite in continuous integration. The test is still part of the overall `damp` suite by default, there is no action needed to ensure that.
Then we can run our test with:
```
./mach talos-test --suite damp --subtest inspector.click
```