✅ test withResolvers()

If we want to backport `withResolvers()` to v3, it will need to have
tests in order to ensure that it behaves the same even though the
implementation will be significantly different

test/with-resolvers.test.ts

@@ -0,0 +1,32 @@
+import { run, withResolvers } from "../mod.ts";
+import { describe, expect, it } from "./suite.ts";
+
+describe("withResolvers()", () => {
+  it("resolves", async () => {
+    let { operation, resolve } = withResolvers<string>();
+    resolve("hello");
+    await expect(run(() => operation)).resolves.toEqual("hello");
+  });
+  it("resolves only once", async () => {
+    let { operation, resolve, reject } = withResolvers<string>();
+    resolve("hello");
+    reject(new Error("boom!"));
+    resolve("goodbye");
+    await expect(run(() => operation)).resolves.toEqual("hello");
+  });
+  it("rejects", async () => {
+    let { operation, reject } = withResolvers<string>();
+    reject(new Error("boom!"));
+    await expect(run(() => operation)).rejects.toMatchObject({
+      message: "boom!",
+    });
+  });
+  it("rejects only once", async () => {
+    let { operation, reject } = withResolvers<string>();
+    reject(new Error("boom!"));
+    reject(new Error("bam!"));
+    await expect(run(() => operation)).rejects.toMatchObject({
+      message: "boom!",
+    });
+  });
+});