FlowTracer In Vitest

A FlowTracer unit-test capture has two independent parts:

1. The Vite plugin transforms the application source under test.
2. A Vitest setup file loads the Flow runtime before the transformed module executes.

The browser runtime injection performed through Vite HTML is not part of a Node-based Vitest run. Load @autotracer/flow/runtime explicitly for this workflow.

Add A Capture Mode

Configure a dedicated mode so ordinary test runs remain uninstrumented. Merge with existing plugins and setup files:

// vitest.config.ts
import { flowTracer } from "@autotracer/plugin-vite-flow";
import { defineConfig } from "vitest/config";

export default defineConfig(({ mode }) => {
  const captureWithAutoTracer = mode === "autotracer";

  return {
    plugins: captureWithAutoTracer ? [
      flowTracer({
        include: {
          paths: ["**/src/domain/**"],
        },
      }),
    ] : [],
    test: {
      setupFiles: captureWithAutoTracer
        ? ["./test/autotracer.setup.ts"]
        : [],
    },
  };
});

Use a glob such as **/src/domain/** that matches the source under test. FlowTracer normalizes transformed file paths to forward slashes before matching.

Load The Runtime

// test/autotracer.setup.ts
import "@autotracer/flow/runtime";

const autoTracer = Reflect.get(globalThis, "autoTracer");

autoTracer.setOutputMode("copy-paste");

The runtime starts dormant. The setup file runs before test modules in capture mode. Do not import it from the test body: doing so would also load the runtime in ordinary test runs.

Bracket One Operation

import { describe, expect, it } from "vitest";
import { calculateTotal } from "../src/domain/calculateTotal";

describe("calculateTotal", () => {
  it("applies the discount", () => {
    const flow = Reflect.get(globalThis, "autoTracer")?.flowTracer;
    flow?.start();

    try {
      const total = calculateTotal([20, 30], 0.1);
      expect(total).toBe(45);
    } finally {
      flow?.stop();
    }
  });
});

Run only the relevant test in the capture mode:

pnpm exec vitest run --mode autotracer test/calculateTotal.test.ts

The trace is written to the Vitest process output. In copy-paste mode it is text-shaped and can be copied directly.

Verify that calculateTotal appears in the output; the application assertion can pass even if instrumentation is missing. Preserve that output and explain its inputs and returns. Await asynchronous operations inside the try block before stopping.

Scope Of The Capture

• Only source selected by the Flow build transform can emit trace output.
• Test files and test directories are excluded by the plugin defaults. The usual target is application or library source invoked by the test, not the test body itself.
• Keep the include.paths list narrow and run a single test while investigating.
• Call stop() in cleanup so a failed assertion does not leave tracing enabled for a later test.

For transform settings, see the Flow Vite Plugin API. For runtime controls, see the Flow Runtime API. To interpret the output, see Analyze A Trace.