04/02: add expect scoping to the exercise

Author: kettanaito

exercises/04.performance/02.problem.concurrency/src/one.test.ts

@@ -3,7 +3,11 @@ import { setTimeout } from 'node:timers/promises'
 for (let i = 0; i < 100; i++) {
 	// 🐨 Replace the `test()` function below with `test.concurrent()`.
 	// This will make all the test cases in this test file run simultaneously.
-	test(`${i}`, async ({ expect }) => {
+	//
+	// 🐨 Spread the test context argument here and reference the `expect`
+	// function from that object.
+	// 💰 async ({ expect }) => {}
+	test(`${i}`, async () => {
 		await setTimeout(25)
 		expect(i).toBe(i)
 	})

exercises/04.performance/02.problem.concurrency/src/two.test.ts

@@ -3,7 +3,11 @@ import { setTimeout } from 'node:timers/promises'
 for (let i = 0; i < 100; i++) {
 	// 🐨 Replace the `test()` function below with `test.concurrent()`.
 	// This will make all the test cases in this test file run simultaneously.
-	test(`${i}`, async ({ expect }) => {
+	//
+	// 🐨 Spread the test context argument here and reference the `expect`
+	// function from that object.
+	// 💰 async ({ expect }) => {}
+	test(`${i}`, async () => {
 		await setTimeout(25)
 		expect(i).toBe(i)
 	})

exercises/04.performance/02.solution.concurrency/README.mdx

@@ -4,7 +4,7 @@ Vitest runs each test case in a test file _sequentially_. We can speed up our te
 
 ```diff filename=your.test.ts remove=1 add=2
 test(`${i}`, () => {})
-test.concurrent(`${i}`, () => {})
+test.concurrent(`${i}`, async () => {})
 //   👆👆👆👆👆👆
 ```
 
@@ -14,7 +14,7 @@ By making our test cases concurrent, we can switch from a test waterfall to a fl
 
 Now that our test run at the same time, it is absolutely crucial we provision proper _test isolation_. We don't want tests to be stepping on each other's toes and becoming flaky as a result. This often comes down to eliminating or replacing any shared (or global) state in test cases.
 
-For example, ...
+For example, the `expect()` function that you use to make assertions _might contain state_. It is essential we scoped that function to individual test case by accessing it from the test context object:
 
 ```ts diff remove=1 add=3
 test.concurrent(`${i}`, async () => {