test: cut low-value tests, rewrite the rest around behavior, parallelize lanes (#285)

launcher/test-support/env.ts

@@ -0,0 +1,25 @@
+/**
+ * Runs `run` with the given process env values (`undefined` deletes a key) and restores the
+ * originals afterwards, even if `run` throws or rejects.
+ */
+export async function withEnv<T>(
+  overrides: Record<string, string | undefined>,
+  run: () => T | Promise<T>,
+): Promise<T> {
+  const originals = Object.fromEntries(
+    Object.keys(overrides).map((key) => [key, process.env[key]]),
+  );
+  const apply = (values: Record<string, string | undefined>): void => {
+    for (const [key, value] of Object.entries(values)) {
+      if (value === undefined) delete process.env[key];
+      else process.env[key] = value;
+    }
+  };
+
+  apply(overrides);
+  try {
+    return await run();
+  } finally {
+    apply(originals);
+  }
+}