test(gh-design): add filterReviewers unit tests

Extract reviewer filtering into a testable pure function and add
tests covering: self-authored PRs, already-requested reviewers,
empty reviewer lists, and undefined alreadyRequested.

Amp-Thread-ID: https://ampcode.com/threads/T-019ddde1-db08-71ca-809d-fd7e51b68842
Co-authored-by: Amp <amp@ampcode.com>

Author: snomiao

app/tasks/gh-design/filterReviewers.spec.ts

@@ -0,0 +1,41 @@
+import { describe, expect, it } from "bun:test";
+import { filterReviewers } from "./gh-design";
+
+describe("filterReviewers", () => {
+  const REVIEWERS = ["PabloWiedemann", "AliceDev"];
+
+  it("excludes the PR author from both lists", () => {
+    const result = filterReviewers(REVIEWERS, "PabloWiedemann");
+    expect(result.requestReviewers).toEqual(["AliceDev"]);
+    expect(result.newReviewers).toEqual(["AliceDev"]);
+  });
+
+  it("returns all reviewers when author is not in the list", () => {
+    const result = filterReviewers(REVIEWERS, "SomeoneElse");
+    expect(result.requestReviewers).toEqual(["PabloWiedemann", "AliceDev"]);
+    expect(result.newReviewers).toEqual(["PabloWiedemann", "AliceDev"]);
+  });
+
+  it("excludes already-requested reviewers from newReviewers only", () => {
+    const result = filterReviewers(REVIEWERS, "SomeoneElse", ["PabloWiedemann"]);
+    expect(result.requestReviewers).toEqual(["PabloWiedemann", "AliceDev"]);
+    expect(result.newReviewers).toEqual(["AliceDev"]);
+  });
+
+  it("returns empty newReviewers when all are already requested", () => {
+    const result = filterReviewers(REVIEWERS, "SomeoneElse", ["PabloWiedemann", "AliceDev"]);
+    expect(result.requestReviewers).toEqual(["PabloWiedemann", "AliceDev"]);
+    expect(result.newReviewers).toEqual([]);
+  });
+
+  it("returns empty lists when author is the only reviewer", () => {
+    const result = filterReviewers(["PabloWiedemann"], "PabloWiedemann");
+    expect(result.requestReviewers).toEqual([]);
+    expect(result.newReviewers).toEqual([]);
+  });
+
+  it("handles undefined alreadyRequested as no-one requested yet", () => {
+    const result = filterReviewers(REVIEWERS, "SomeoneElse", undefined);
+    expect(result.newReviewers).toEqual(["PabloWiedemann", "AliceDev"]);
+  });
+});

app/tasks/gh-design/gh-design.ts

@@ -95,6 +95,20 @@ type GithubDesignTask = {
   lastDoneAt?: Date | null; // last time this item was processed successfuly
 };
 
+/**
+ * Filter the reviewer list for a PR: excludes the PR author and
+ * anyone who has already been requested.
+ */
+export function filterReviewers(
+  allReviewers: string[],
+  prAuthor: string,
+  alreadyRequested?: string[],
+): { requestReviewers: string[]; newReviewers: string[] } {
+  const requestReviewers = allReviewers.filter((e) => e !== prAuthor);
+  const newReviewers = requestReviewers.filter((e) => !alreadyRequested?.includes(e));
+  return { requestReviewers, newReviewers };
+}
+
 // task states
 const COLLECTION_NAME = "GithubDesignTask";
 export const GithubDesignTaskMeta = TaskMetaCollection(COLLECTION_NAME, githubDesignTaskMetaSchema);
@@ -258,9 +272,10 @@ export async function runGithubDesignTask() {
           task.type === "pull_request" &&
           REQUEST_REVIEWERS.some((e) => !task.reviewers?.includes(e))
         ) {
-          const requestReviewers = REQUEST_REVIEWERS.filter((e) => e !== task.user);
-          const newReviewers = requestReviewers.filter(
-            (e) => !task.reviewers?.includes(e),
+          const { requestReviewers, newReviewers } = filterReviewers(
+            REQUEST_REVIEWERS,
+            task.user,
+            task.reviewers,
           );
           tlog(`Requesting reviewers: ${newReviewers.join(", ") || "(none)"}`);
           if (!dryRun) {