feat: add parameter for test name of each

docs/api/index.md

@@ -121,22 +121,33 @@ For compatibility with Jest, `TestFunction` can also be of type `(done: DoneCall
 - **Type:** `(cases: ReadonlyArray<T>) => void`
 - **Alias:** `it.each`
 
-Use `test.each` when you need to run the same test with different variables.
-You can use `%i` or `%s` in the test name in the order of the test function parameters.
-```ts
-test.each([
-  [1, 1, 2],
-  [1, 2, 3],
-  [2, 1, 3],
-])('add(%i, %i) -> %i', (a, b, expected) => {
-  expect(a + b).toBe(expected)
-})
-
-// this will return
-// √ add(1, 1) -> 2
-// √ add(1, 2) -> 3
-// √ add(2, 1) -> 3
-```
+  Use `test.each` when you need to run the same test with different variables.  
+  You can inject parameters with [printf formmatting](https://nodejs.org/api/util.html#util_util_format_format_args) in the test name in the order of the test function parameters.
+
+  - `%s`: string
+  - `%d`: number
+  - `%i`: integer
+  - `%f`: floating point value
+  - `%j`: json
+  - `$o`: object
+  - `%#`: index of the test case
+  - `%%`: single precent sign ('%')
+
+  ```ts
+  test.each([
+    [1, 1, 2],
+    [1, 2, 3],
+    [2, 1, 3],
+  ])('add(%i, %i) -> %i', (a, b, expected) => {
+    expect(a + b).toBe(expected)
+  })
+
+  // this will return
+  // √ add(1, 1) -> 2
+  // √ add(1, 2) -> 3
+  // √ add(2, 1) -> 3
+  ```
+
 ## describe
 
 When you use `test` in the top level of file, they are collected as part of the implicit suite for it. Using `describe` you can define a new suite in the current context, as a set of related tests and other nested suites. A suite lets you organize your tests so reports are more clear.

packages/vitest/src/runtime/suite.ts

@@ -14,7 +14,15 @@ export const test = createTest(
   },
 )
 
-function formatTitle(template: string, items: any[]) {
+function formatTitle(template: string, items: any[], idx: number) {
+  if (template.includes('%#')) {
+    // '%#' match index of the test case
+    template = template
+      .replace(/%%/g, '__vitest_escaped_%__')
+      .replace(/%#/g, `${idx}`)
+      .replace(/__vitest_escaped_%__/g, '%%')
+  }
+
   const count = template.split('%').length - 1
   let formatted = format(template, ...items.slice(0, count))
   if (isObject(items[0])) {
@@ -146,9 +154,9 @@ function createSuite() {
 
   suite.each = <T>(cases: ReadonlyArray<T>) => {
     return (name: string, fn: (...args: T[]) => void) => {
-      cases.forEach((i) => {
+      cases.forEach((i, idx) => {
         const items = toArray(i) as any
-        suite(formatTitle(name, items), () => fn(...items))
+        suite(formatTitle(name, items, idx), () => fn(...items))
       })
     }
   }
@@ -164,9 +172,9 @@ function createTest(fn: ((this: Record<'concurrent'| 'skip'| 'only'| 'todo'| 'fa
 
   test.each = <T>(cases: ReadonlyArray<T>) => {
     return (name: string, fn: (...args: T[]) => void) => {
-      cases.forEach((i) => {
+      cases.forEach((i, idx) => {
         const items = toArray(i) as any
-        test(formatTitle(name, items), () => fn(...items))
+        test(formatTitle(name, items, idx), () => fn(...items))
       })
     }
   }

test/core/test/each.test.ts

@@ -75,3 +75,11 @@ describe.each([1, 2, 0])('%s (describe.each 1d)', (num) => {
     expect(typeof num).toEqual('number')
   })
 })
+
+test.each([
+  [1, 1, 2],
+  [1, 2, 3],
+  [2, 1, 3],
+])('the index of the test case is %#', (a, b, expected) => {
+  expect(a + b).toBe(expected)
+})