angular/angular-cli · warning

Project "${projectName}" uses a custom Karma configuration f

Error message

Project "${projectName}" uses a custom Karma configuration file "${karmaConfig}". Tests have been migrated to use Vitest, but you may need to manually migrate custom settings from this Karma config to a Vitest config (e.g. "vitest-base.config.ts") and set the "runnerConfig" option to true.

What it means

The Karma-to-Vitest migration can translate the builder options, but when a project points at a custom karma.conf.js that the processor cannot fully remove or translate, it warns that manual migration of custom settings into a Vitest config (e.g. vitest-base.config.ts) is required, and that the 'runnerConfig' option should be set to true.

Source

Thrown at packages/schematics/angular/migrations/migrate-karma-to-vitest/karma-processor.ts:163

      const diff = await compareKarmaConfigToDefault(
        analysis,
        projectName,
        karmaConfig,
        needDevkitPlugin,
      );
      isRemovable = !hasDifferences(diff) && diff.isReliable;
    }

    cachedResult = { analysis, isRemovable };
    cache.set(karmaConfig, cachedResult);
  }

  if (cachedResult) {
    extractReporters(cachedResult.analysis, options, projectName, context);
    extractCoverageSettings(cachedResult.analysis, options, projectName, context);

    if (!cachedResult.isRemovable) {
      context.logger.warn(
        `Project "${projectName}" uses a custom Karma configuration file "${karmaConfig}". ` +
          `Tests have been migrated to use Vitest, but you may need to manually migrate custom settings ` +
          `from this Karma config to a Vitest config (e.g. "vitest-base.config.ts") ` +
          `and set the "runnerConfig" option to true.`,
      );
      manualMigrationFiles.push(karmaConfig);
    }
  }

  delete options['karmaConfig'];
}

View on GitHub (pinned to bb72145f9a)

Solutions

1. Review the custom karma.conf.js and port each custom setting (plugins, proxies, middleware, files, preprocessors) into your Vitest config (e.g. vitest-base.config.ts)
2. Set "runnerConfig": true on the test target options so Vitest uses your custom config
3. Remove the now-unused karma.conf.js once settings are ported
4. Run your test suite to confirm behavior matches the previous Karma setup

Example fix

// before (angular.json test target)
"karmaConfig": "src/karma.conf.js"
// after
"runnerConfig": true,
// plus a vitest-base.config.ts containing the ported custom settings

// before migrating, flag custom karma configs for manual porting
const opts = angularJson.projects[proj].architect?.test?.options || {};
if (opts.karmaConfig) {
  console.warn(`${proj} uses custom karma config ${opts.karmaConfig}; plan to port settings to a Vitest config and set runnerConfig: true`);
}

When it happens

Trigger: Running processKarmaConfig during the migrate-karma-to-vitest migration when the project's test target specifies a custom karmaConfig file whose parsed analysis is not flagged as removable (custom plugins, frameworks, middlewares, proxies, etc.).

Common situations: Large Angular workspaces with hand-tuned karma.conf.js (webpack customizations, coverage thresholds, custom reporters, proxies) migrating tests to Vitest during an Angular CLI version migration.

Related errors

• - ${file}
• Project "${projectName}" uses a custom coverage reporter "${
• The following Karma configuration files require manual migr
• No "test" target found for project "${options.project}". A "
• Cannot add a Vitest configuration as builder for "test" targ

AI-assisted analysis of angular/angular-cli@bb72145f9a (2026-08-30). Data as JSON: /api/errors/549b6e5ddeaae94b. Report an issue: GitHub.