fix(watch): run test files when added to filesystem

packages/vitest/src/node/core.ts

@@ -592,6 +592,8 @@ export class Vitest {
       id = slash(id)
       updateLastChanged(id)
       if (await this.isTargetFile(id)) {
+        this.projectsTestFiles.set(id, new Set(this.projects))
+
         this.changedTests.add(id)
         this.scheduleRerun([id])
       }

test/watch/test/file-watching.test.ts

@@ -1,4 +1,4 @@
-import { readFileSync, writeFileSync } from 'node:fs'
+import { readFileSync, rmSync, writeFileSync } from 'node:fs'
 import { afterEach, describe, test } from 'vitest'
 
 import { startWatchMode } from './utils'
@@ -12,6 +12,8 @@ const testFileContent = readFileSync(testFile, 'utf-8')
 const configFile = 'fixtures/vitest.config.ts'
 const configFileContent = readFileSync(configFile, 'utf-8')
 
+const cleanups: (() => void)[] = []
+
 function editFile(fileContent: string) {
   return `// Modified by file-watching.test.ts
 ${fileContent}
@@ -23,6 +25,7 @@ afterEach(() => {
   writeFileSync(sourceFile, sourceFileContent, 'utf8')
   writeFileSync(testFile, testFileContent, 'utf8')
   writeFileSync(configFile, configFileContent, 'utf8')
+  cleanups.splice(0).forEach(cleanup => cleanup())
 })
 
 test('editing source file triggers re-run', async () => {
@@ -64,6 +67,26 @@ test('editing config file reloads new changes', async () => {
   await vitest.waitForOutput('ok 2')
 })
 
+test('adding a new test file triggers re-run', async () => {
+  const vitest = await startWatchMode()
+
+  const testFile = 'fixtures/new-dynamic.test.ts'
+  const testFileContent = `
+import { expect, test } from "vitest";
+
+test("dynamic test case", () => {
+  console.log("Running added dynamic test")
+  expect(true).toBeTruthy()
+})
+`
+  cleanups.push(() => rmSync(testFile))
+  writeFileSync(testFile, testFileContent, 'utf-8')
+
+  await vitest.waitForOutput('Running added dynamic test')
+  await vitest.waitForOutput('RERUN  ../new-dynamic.test.ts')
+  await vitest.waitForOutput('1 passed')
+})
+
 describe('browser', () => {
   test.runIf((process.platform !== 'win32'))('editing source file triggers re-run', async () => {
     const vitest = await startWatchMode('--browser.enabled', '--browser.headless', '--browser.name=chrome')