feat(experimental): print how many tests were affected and a total when running --changed

packages/vitest/src/node/core.ts

@@ -151,6 +151,7 @@ export class Vitest {
 
   /** @internal */ configOverride: Partial<ResolvedConfig> = {}
   /** @internal */ filenamePattern?: string[]
+  /** @internal */ _sourceFilterResult?: { affected: number; total: number }
   /** @internal */ runningPromise?: Promise<TestRunResult>
   /** @internal */ closingPromise?: Promise<void>
   /** @internal */ cancelPromise?: Promise<void | void[]>
@@ -1102,6 +1103,7 @@ export class Vitest {
         // all subsequent runs will treat this as a fresh run
         this.config.changed = false
         this.config.related = undefined
+        this._sourceFilterResult = undefined
       })
 
       return await this.runningPromise
@@ -1301,6 +1303,7 @@ export class Vitest {
       // all subsequent runs will treat this as a fresh run
       this.config.changed = false
       this.config.related = undefined
+      this._sourceFilterResult = undefined
     })
 
     return await this.runningPromise

packages/vitest/src/node/reporters/base.ts

@@ -54,6 +54,7 @@ import {
   formatTimeString,
   getStateString,
   getStateSymbol,
+  noun,
   padSummaryTitle,
   renderSnapshotSummary,
   separator,
@@ -659,6 +660,25 @@ export abstract class BaseReporter implements Reporter {
     this.reportTestSummary(files, errors, leakCount)
   }
 
+  private printSourceFilterSummary(): void {
+    const result = this.ctx._sourceFilterResult
+    const related = this.ctx.config.related
+    if (!result || !related) {
+      return
+    }
+
+    const sources =
+      related.length === 1 && !this.ctx.config.changed
+        ? relative(this.ctx.config.root, related[0])
+        : `${related.length} ${this.ctx.config.changed ? 'changed ' : ''}${noun(related.length, 'file', 'files')}`
+
+    this.log(
+      padSummaryTitle('Affected'),
+      `${result.affected} of ${result.total} test files`,
+      c.dim(`(related to ${sources})`),
+    )
+  }
+
   reportTestSummary(files: File[], errors: unknown[], leakCount: number): void {
     this.log()
 
@@ -677,6 +697,7 @@ export abstract class BaseReporter implements Reporter {
     }
 
     this.log(padSummaryTitle('Test Files'), getStateString(affectedFiles))
+    this.printSourceFilterSummary()
     this.log(padSummaryTitle('Tests'), getStateString(tests))
 
     if (this.ctx.projects.some((c) => c.config.typecheck.enabled)) {

packages/vitest/src/node/specifications.ts

@@ -117,6 +117,8 @@ export class VitestSpecifications {
   }
 
   private async filterTestsBySource(specs: TestSpecification[]): Promise<TestSpecification[]> {
+    this.vitest._sourceFilterResult = undefined
+
     if (this.vitest.config.changed && !this.vitest.config.related) {
       const related = await this.vitest.vcs.findChangedFiles({
         root: this.vitest.config.root,
@@ -157,7 +159,11 @@ export class VitestSpecifications {
       affectedByProject.set(project, await this.getAffectedModules(project, projectSpecs, related))
     }
 
-    return specs.filter((spec) => affectedByProject.get(spec.project)!.has(spec.moduleId))
+    const affectedSpecs = specs.filter((spec) =>
+      affectedByProject.get(spec.project)!.has(spec.moduleId),
+    )
+    this.vitest._sourceFilterResult = { affected: affectedSpecs.length, total: specs.length }
+    return affectedSpecs
   }
 
   /**

test/e2e/test/vcs-provider.test.ts

@@ -4,8 +4,12 @@ import { expect, onTestFinished, test, vi } from 'vitest'
 import { createVitest } from 'vitest/node'
 import { runInlineTests, useFS } from '#test-utils'
 
+function affectedSummary(stdout: string) {
+  return stdout.split('\n').find((line) => line.includes('Affected'))
+}
+
 test('custom vcsProvider that returns specific files runs only matching tests', async () => {
-  const { testTree, stderr } = await runInlineTests(
+  const { testTree, stderr, stdout } = await runInlineTests(
     {
       'vitest.config.js': `
       import path from 'node:path'
@@ -51,6 +55,47 @@ test('custom vcsProvider that returns specific files runs only matching tests',
       },
     }
   `)
+  expect(affectedSummary(stdout)).toMatchInlineSnapshot(
+    `"   Affected  1 of 2 test files (related to 1 changed file)"`,
+  )
+})
+
+test('related prints how many test files were affected', async () => {
+  const { testTree, stderr, stdout } = await runInlineTests(
+    {
+      'src/changed.ts': 'export const a = 1',
+      'src/not-changed.ts': 'export const b = 2',
+      'related.test.ts': `
+      import { a } from './src/changed.ts'
+      import { test, expect } from 'vitest'
+      test('related test', () => {
+        expect(a).toBe(1)
+      })
+    `,
+      'not-related.test.ts': `
+      import { b } from './src/not-changed.ts'
+      import { test, expect } from 'vitest'
+      test('not related test', () => {
+        expect(b).toBe(2)
+      })
+    `,
+    },
+    {
+      related: ['src/changed.ts'],
+    },
+  )
+
+  expect(stderr).toBe('')
+  expect(testTree()).toMatchInlineSnapshot(`
+    {
+      "related.test.ts": {
+        "related test": "passed",
+      },
+    }
+  `)
+  expect(affectedSummary(stdout)).toMatchInlineSnapshot(
+    `"   Affected  1 of 2 test files (related to src/changed.ts)"`,
+  )
 })
 
 test('custom vcsProvider that returns no files runs no tests', async () => {