fix: Better error handling on no test code.

src/worker.ts

@@ -168,7 +168,13 @@ export function runWorker(context: WorkerContext, notifier: (value: any) => void
   const { warmup, tests, index, iterations, errorThreshold } = context
 
   // Require the original file to build tests
-  const [name, testDefinition] = tests[index]
+  const testToRun = tests?.[index]
+
+  if (!testToRun) {
+    throw new Error('No test code exported from the worker thread')
+  }
+
+  const [name, testDefinition] = testToRun
 
   // Prepare the test
   let test: TestFunction = noOp

test/notTestExportedInWorkers.test.ts

@@ -0,0 +1,38 @@
+import { deepStrictEqual, ok } from 'node:assert'
+import { test } from 'node:test'
+import { isMainThread } from 'node:worker_threads'
+import { cronometro } from '../src/index.js'
+
+if (isMainThread) {
+  test('Errors are properly handled when no tests are exported in the worker threads', async () => {
+    const results = await cronometro(
+      {
+        single() {},
+        multiple() {}
+      },
+      { iterations: 10, print: false }
+    )
+
+    ok(!results.single.success)
+    ok(results.single.error instanceof Error)
+    deepStrictEqual(results.single.error.message, 'No test code exported from the worker thread')
+    deepStrictEqual(results.single.size, 0)
+    deepStrictEqual(results.single.min, 0)
+    deepStrictEqual(results.single.max, 0)
+    deepStrictEqual(results.single.mean, 0)
+    deepStrictEqual(results.single.stddev, 0)
+    deepStrictEqual(results.single.standardError, 0)
+    deepStrictEqual(results.single.percentiles, {})
+
+    ok(!results.multiple.success)
+    ok(results.multiple.error instanceof Error)
+    deepStrictEqual(results.multiple.error.message, 'No test code exported from the worker thread')
+    deepStrictEqual(results.multiple.size, 0)
+    deepStrictEqual(results.multiple.min, 0)
+    deepStrictEqual(results.multiple.max, 0)
+    deepStrictEqual(results.multiple.mean, 0)
+    deepStrictEqual(results.multiple.stddev, 0)
+    deepStrictEqual(results.multiple.standardError, 0)
+    deepStrictEqual(results.multiple.percentiles, {})
+  })
+}