Add package @cosmjs/utils

packages/utils/src/assert.ts

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+export function assert(condition: any, msg?: string): asserts condition {
+  if (!condition) {
+    throw new Error(msg || "condition is not truthy");
+  }
+}

packages/utils/src/index.ts

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+export { assert } from "./assert";
+export { sleep } from "./sleep";

packages/utils/src/sleep.spec.ts

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+import { sleep } from "./sleep";
+
+describe("sleep", () => {
+  it("resolves after at least x milliseconds", async () => {
+    for (const x of [10, 30, 120, 280]) {
+      const start = Date.now();
+      await sleep(x);
+      const sleepingTime = Date.now() - start;
+
+      // Add 1 ms safety margin due to rounding issues. The elapsed time between
+      // timestamps 1000 and 1010 can be somethting between 10 and 11 ms.
+      expect(sleepingTime + 1).toBeGreaterThanOrEqual(x);
+    }
+  });
+
+  it("resolves within a reasonable amount of time >= x milliseconds", async () => {
+    // Don't be too strict as jest will run many tests at the same time and test systems can be slow sometimes.
+    const tolerance = 30; // ms
+
+    for (const x of [10, 30, 120, 280]) {
+      const start = Date.now();
+      await sleep(x);
+      const sleepingTime = Date.now() - start;
+      expect(sleepingTime).toBeLessThanOrEqual(x + tolerance);
+    }
+  });
+});

packages/utils/src/sleep.ts

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+export async function sleep(ms: number): Promise<void> {
+  return new Promise((resolve) => setTimeout(resolve, ms));
+}