Why I Migrated From Jest to Vitest

Two packages I needed were ESM-only. Jest could not load them. I tried transformIgnorePatterns. It partially worked for one but not the other. Switched to Vitest. Everything worked immediately.

Uninstalled Jest. Installed Vitest. Rewrote configs.

// vitest.unit.config.ts
import { defineConfig, mergeConfig } from "vitest/config";
import baseConfig from "./vitest.base";

export default mergeConfig(
  baseConfig,
  defineConfig({
    test: { include: ["src/**/*.unit.spec.ts"] },
  }),
);

Unit config uses the default threads pool. Fast, no Docker.

// vitest.it.config.ts
import { defineConfig, mergeConfig } from "vitest/config";
import baseConfig from "./vitest.base";

export default mergeConfig(
  baseConfig,
  defineConfig({
    test: {
      include: ["test/**/*.it.spec.ts"],
      pool: "forks",
      testTimeout: 120_000,
    },
  }),
);

Unit and integration configs split by include pattern. Same assertions. Different imports. Auth tests passed immediately. CI scripts changed from jest to vitest.

One gotcha: Nest’s tsconfig.build.json does not exclude vitest*.ts by default. The import.meta in vitest configs breaks the build. Added it manually.

{
  "exclude": ["node_modules", "dist", "vitest*.ts"]
}