Extending Reporters 
WARNING
This is an advanced API. If you just want to configure built-in reporters, read the "Reporters" guide.
You can import reporters from vitest/reporters and extend them to create your custom reporters.
Extending Built-in Reporters 
In general, you don't need to create your reporter from scratch. vitest comes with several default reporting programs that you can extend.
import { DefaultReporter } from 'vitest/reporters'
export default class MyDefaultReporter extends DefaultReporter {
  // do something
}Of course, you can create your reporter from scratch. Just extend the BaseReporter class and implement the methods you need.
And here is an example of a custom reporter:
import { BaseReporter } from 'vitest/reporters'
export default class CustomReporter extends BaseReporter {
  onTestModuleCollected() {
    const files = this.ctx.state.getFiles(this.watchFilters)
    this.reportTestSummary(files)
  }
}Or implement the Reporter interface:
import type { Reporter } from 'vitest/node'
export default class CustomReporter implements Reporter {
  onTestModuleCollected() {
    // print something
  }
}Then you can use your custom reporter in the vitest.config.ts file:
import { defineConfig } from 'vitest/config'
import CustomReporter from './custom-reporter.js'
export default defineConfig({
  test: {
    reporters: [new CustomReporter()],
  },
})Reported Tasks 
Instead of using the tasks that reporters receive, it is recommended to use the Reported Tasks API instead.
You can get access to this API by calling vitest.state.getReportedEntity(runnerTask):
import type { Reporter, TestModule } from 'vitest/node'
class MyReporter implements Reporter {
  onTestRunEnd(testModules: ReadonlyArray<TestModule>) {
    for (const testModule of testModules) {
      for (const task of testModule.children) {
        console.log('test run end', task.type, task.fullName)
      }
    }
  }
}Exported Reporters 
vitest comes with a few built-in reporters that you can use out of the box.
Built-in reporters: 
DefaultReporterDotReporterJsonReporterVerboseReporterTapReporterJUnitReporterTapFlatReporterHangingProcessReporterTreeReporter
Base Abstract reporters: 
BaseReporter
Interface reporters: 
Reporter