From dd843132f986d501adffa31e7a682fcc88f6c68a Mon Sep 17 00:00:00 2001
From: "glm-5.1" <glm-5.1@alk.dev>
Date: Fri, 8 May 2026 06:07:36 +0000
Subject: [PATCH] feat(core-operators-tests): add comprehensive tests for all
 13 stream operators

53 tests covering filter, map, pipe, take, reduce, toArray, batch,
dedupe, window, flat, groupBy, chain, and join operators including
async predicates/mappers, type-narrowing overloads, edge cases, and
pipe+subscribe composition.
---
 test/operators.test.ts | 511 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 511 insertions(+)
 create mode 100644 test/operators.test.ts

diff --git a/test/operators.test.ts b/test/operators.test.ts
new file mode 100644
index 0000000..63fe7f7
--- /dev/null
+++ b/test/operators.test.ts
@@ -0,0 +1,511 @@
+import { describe, it, expect } from "vitest";
+import {
+  filter,
+  map,
+  pipe,
+  take,
+  reduce,
+  toArray,
+  batch,
+  dedupe,
+  window,
+  flat,
+  groupBy,
+  chain,
+  join,
+} from "../src/operators.js";
+import { createPubSub } from "../src/create_pubsub.js";
+import { Repeater } from "../src/repeater.js";
+
+async function* fromArray<T>(items: T[]): AsyncIterable<T> {
+  for (const item of items) {
+    yield item;
+  }
+}
+
+async function collect<T>(source: AsyncIterable<T>): Promise<T[]> {
+  const result: T[] = [];
+  for await (const item of source) {
+    result.push(item);
+  }
+  return result;
+}
+
+describe("filter", () => {
+  it("filters items by predicate", async () => {
+    const source = fromArray([1, 2, 3, 4, 5]);
+    const result = await collect(filter((x: number) => x % 2 === 0)(source));
+    expect(result).toEqual([2, 4]);
+  });
+
+  it("supports type-narrowing overload", async () => {
+    type Fish = { type: "fish"; swim: boolean };
+    type Bird = { type: "bird"; fly: boolean };
+    type Animal = Fish | Bird;
+
+    const animals: Animal[] = [
+      { type: "fish", swim: true },
+      { type: "bird", fly: true },
+      { type: "fish", swim: false },
+    ];
+    const source = fromArray(animals);
+    const isFish = (a: Animal): a is Fish => a.type === "fish";
+    const result = await collect(filter(isFish)(source));
+    expect(result).toEqual([
+      { type: "fish", swim: true },
+      { type: "fish", swim: false },
+    ]);
+  });
+
+  it("supports async predicate", async () => {
+    const source = fromArray([1, 2, 3, 4, 5]);
+    const result = await collect(
+      filter(async (x: number) => {
+        await Promise.resolve();
+        return x > 3;
+      })(source),
+    );
+    expect(result).toEqual([4, 5]);
+  });
+
+  it("yields nothing when all items are filtered", async () => {
+    const source = fromArray([1, 3, 5]);
+    const result = await collect(filter((x: number) => x % 2 === 0)(source));
+    expect(result).toEqual([]);
+  });
+
+  it("yields all items when nothing is filtered", async () => {
+    const source = fromArray([2, 4, 6]);
+    const result = await collect(filter((x: number) => x % 2 === 0)(source));
+    expect(result).toEqual([2, 4, 6]);
+  });
+});
+
+describe("map", () => {
+  it("transforms items", async () => {
+    const source = fromArray([1, 2, 3]);
+    const result = await collect(map((x: number) => x * 2)(source));
+    expect(result).toEqual([2, 4, 6]);
+  });
+
+  it("supports async mapper", async () => {
+    const source = fromArray([1, 2, 3]);
+    const result = await collect(
+      map(async (x: number) => {
+        await Promise.resolve();
+        return x + 10;
+      })(source),
+    );
+    expect(result).toEqual([11, 12, 13]);
+  });
+
+  it("transforms types", async () => {
+    const source = fromArray([1, 2, 3]);
+    const result = await collect(map((x: number) => `num:${x}`)(source));
+    expect(result).toEqual(["num:1", "num:2", "num:3"]);
+  });
+});
+
+describe("pipe", () => {
+  it("returns input when no functions provided", () => {
+    const result = pipe(42);
+    expect(result).toBe(42);
+  });
+
+  it("composes 1 function", () => {
+    const result = pipe(5, (x: number) => x * 2);
+    expect(result).toBe(10);
+  });
+
+  it("composes 2 functions", () => {
+    const result = pipe(5, (x: number) => x * 2, (x: number) => x + 1);
+    expect(result).toBe(11);
+  });
+
+  it("composes 3 functions", () => {
+    const result = pipe(
+      5,
+      (x: number) => x * 2,
+      (x: number) => x + 1,
+      (x: number) => x * 3,
+    );
+    expect(result).toBe(33);
+  });
+
+  it("composes 4 functions", () => {
+    const result = pipe(
+      5,
+      (x: number) => x * 2,
+      (x: number) => x + 1,
+      (x: number) => x * 3,
+      (x: number) => x - 5,
+    );
+    expect(result).toBe(28);
+  });
+
+  it("composes filter and map with subscribe", async () => {
+    type Events = {
+      message: string;
+    };
+    const pubsub = createPubSub<Events>();
+    const id = "test-id";
+
+    const subscription = pubsub.subscribe("message", id);
+    const filtered = filter((e: { type: string; id: string; payload: string }) => e.payload.startsWith("hello"));
+    const mapped = map((e: { type: string; id: string; payload: string }) => e.payload.toUpperCase());
+
+    const result = pipe(subscription, filtered, mapped);
+    const iterator = result[Symbol.asyncIterator]();
+
+    const results: string[] = [];
+
+    const collectNext = () => iterator.next().then((r) => {
+      if (!r.done) results.push(r.value);
+    });
+
+    void collectNext();
+    void collectNext();
+
+    pubsub.publish("message", id, "hello world");
+    pubsub.publish("message", id, "goodbye");
+    pubsub.publish("message", id, "hello again");
+
+    await new Promise((r) => setTimeout(r, 50));
+    await iterator.return?.();
+
+    expect(results).toEqual(["HELLO WORLD", "HELLO AGAIN"]);
+  });
+});
+
+describe("take", () => {
+  it("yields first N items, then stops", async () => {
+    const source = fromArray([1, 2, 3, 4, 5]);
+    const result = await collect(take(source, 3));
+    expect(result).toEqual([1, 2, 3]);
+  });
+
+  it("yields all items if count exceeds source length", async () => {
+    const source = fromArray([1, 2]);
+    const result = await collect(take(source, 5));
+    expect(result).toEqual([1, 2]);
+  });
+
+  it("yields nothing when count is 0", async () => {
+    const source = fromArray([1, 2, 3]);
+    const result = await collect(take(source, 0));
+    expect(result).toEqual([]);
+  });
+
+  it("works with single item", async () => {
+    const source = fromArray([42]);
+    const result = await collect(take(source, 1));
+    expect(result).toEqual([42]);
+  });
+});
+
+describe("reduce", () => {
+  it("reduces to single value", async () => {
+    const source = fromArray([1, 2, 3, 4]);
+    const result = await reduce(source, (acc: number, val: number) => acc + val, 0);
+    expect(result).toBe(10);
+  });
+
+  it("returns initial value for empty source", async () => {
+    const source = fromArray<number>([]);
+    const result = await reduce(source, (acc: number, val: number) => acc + val, 0);
+    expect(result).toBe(0);
+  });
+
+  it("supports async reducer", async () => {
+    const source = fromArray([1, 2, 3]);
+    const result = await reduce(
+      source,
+      async (acc: number, val: number) => {
+        await Promise.resolve();
+        return acc + val;
+      },
+      0,
+    );
+    expect(result).toBe(6);
+  });
+
+  it("reduces with string concatenation", async () => {
+    const source = fromArray(["a", "b", "c"]);
+    const result = await reduce(source, (acc: string, val: string) => acc + val, "");
+    expect(result).toBe("abc");
+  });
+});
+
+describe("toArray", () => {
+  it("collects all items into array", async () => {
+    const source = fromArray([1, 2, 3]);
+    const result = await toArray(source);
+    expect(result).toEqual([1, 2, 3]);
+  });
+
+  it("returns empty array for empty source", async () => {
+    const source = fromArray<number>([]);
+    const result = await toArray(source);
+    expect(result).toEqual([]);
+  });
+
+  it("preserves order", async () => {
+    const source = fromArray([5, 3, 1, 4, 2]);
+    const result = await toArray(source);
+    expect(result).toEqual([5, 3, 1, 4, 2]);
+  });
+});
+
+describe("batch", () => {
+  it("groups into arrays of size", async () => {
+    const source = fromArray([1, 2, 3, 4, 5, 6]);
+    const result = await collect(batch(source, 2));
+    expect(result).toEqual([[1, 2], [3, 4], [5, 6]]);
+  });
+
+  it("yields remaining items if not a full batch", async () => {
+    const source = fromArray([1, 2, 3, 4, 5]);
+    const result = await collect(batch(source, 2));
+    expect(result).toEqual([[1, 2], [3, 4], [5]]);
+  });
+
+  it("yields single batch when source length equals size", async () => {
+    const source = fromArray([1, 2, 3]);
+    const result = await collect(batch(source, 3));
+    expect(result).toEqual([[1, 2, 3]]);
+  });
+
+  it("yields each item individually when size is 1", async () => {
+    const source = fromArray([1, 2, 3]);
+    const result = await collect(batch(source, 1));
+    expect(result).toEqual([[1], [2], [3]]);
+  });
+
+  it("returns empty for empty source", async () => {
+    const source = fromArray<number>([]);
+    const result = await collect(batch(source, 3));
+    expect(result).toEqual([]);
+  });
+});
+
+describe("dedupe", () => {
+  it("yields only unique items", async () => {
+    const source = fromArray([1, 2, 2, 3, 1, 4, 3]);
+    const result = await collect(dedupe(source));
+    expect(result).toEqual([1, 2, 3, 4]);
+  });
+
+  it("yields all items when no duplicates", async () => {
+    const source = fromArray([1, 2, 3]);
+    const result = await collect(dedupe(source));
+    expect(result).toEqual([1, 2, 3]);
+  });
+
+  it("returns empty for empty source", async () => {
+    const source = fromArray<number>([]);
+    const result = await collect(dedupe(source));
+    expect(result).toEqual([]);
+  });
+
+  it("handles all same values", async () => {
+    const source = fromArray([5, 5, 5, 5]);
+    const result = await collect(dedupe(source));
+    expect(result).toEqual([5]);
+  });
+});
+
+describe("window", () => {
+  it("produces sliding window of size with default step 1", async () => {
+    const source = fromArray([1, 2, 3, 4, 5]);
+    const result = await collect(window(source, 3));
+    expect(result).toEqual([[1, 2, 3], [2, 3, 4], [3, 4, 5]]);
+  });
+
+  it("advances by step greater than 1", async () => {
+    const source = fromArray([1, 2, 3, 4, 5, 6]);
+    const result = await collect(window(source, 3, 2));
+    expect(result).toEqual([[1, 2, 3], [3, 4, 5]]);
+  });
+
+  it("yields nothing when source is shorter than window size", async () => {
+    const source = fromArray([1, 2]);
+    const result = await collect(window(source, 3));
+    expect(result).toEqual([]);
+  });
+
+  it("yields single window when source length equals size", async () => {
+    const source = fromArray([1, 2, 3]);
+    const result = await collect(window(source, 3));
+    expect(result).toEqual([[1, 2, 3]]);
+  });
+
+  it("returns empty for empty source", async () => {
+    const source = fromArray<number>([]);
+    const result = await collect(window(source, 2));
+    expect(result).toEqual([]);
+  });
+});
+
+describe("flat", () => {
+  it("flattens AsyncIterable<T[]> into AsyncIterable<T>", async () => {
+    async function* arrays() {
+      yield [1, 2];
+      yield [3, 4];
+      yield [5];
+    }
+    const result = await collect(flat(arrays()));
+    expect(result).toEqual([1, 2, 3, 4, 5]);
+  });
+
+  it("handles empty inner arrays", async () => {
+    async function* arrays() {
+      yield [1, 2];
+      yield [] as number[];
+      yield [3];
+    }
+    const result = await collect(flat(arrays()));
+    expect(result).toEqual([1, 2, 3]);
+  });
+
+  it("returns empty for empty source", async () => {
+    async function* arrays() {
+      // empty
+    }
+    const result = await collect(flat(arrays()));
+    expect(result).toEqual([]);
+  });
+});
+
+describe("groupBy", () => {
+  it("groups items by key into Map", async () => {
+    const source = fromArray([
+      { name: "alice", dept: "eng" },
+      { name: "bob", dept: "eng" },
+      { name: "carol", dept: "sales" },
+    ]);
+    const result = await groupBy(source, (v: { name: string; dept: string }) => v.dept);
+    expect(result.get("eng")).toEqual([
+      { name: "alice", dept: "eng" },
+      { name: "bob", dept: "eng" },
+    ]);
+    expect(result.get("sales")).toEqual([{ name: "carol", dept: "sales" }]);
+  });
+
+  it("returns empty Map for empty source", async () => {
+    const source = fromArray<number>([]);
+    const result = await groupBy(source, (v: number) => v);
+    expect(result.size).toBe(0);
+  });
+
+  it("groups with numeric keys", async () => {
+    const source = fromArray([1, 2, 3, 4, 5, 6]);
+    const result = await groupBy(source, (v: number) => v % 2);
+    expect(result.get(0)).toEqual([2, 4, 6]);
+    expect(result.get(1)).toEqual([1, 3, 5]);
+  });
+});
+
+describe("chain", () => {
+  it("concatenates multiple async iterables", async () => {
+    const source = chain(fromArray([1, 2]), fromArray([3, 4]), fromArray([5]));
+    const result = await collect(source);
+    expect(result).toEqual([1, 2, 3, 4, 5]);
+  });
+
+  it("handles single iterable", async () => {
+    const source = chain(fromArray([1, 2, 3]));
+    const result = await collect(source);
+    expect(result).toEqual([1, 2, 3]);
+  });
+
+  it("handles empty iterables", async () => {
+    const source = chain(fromArray<number>([]), fromArray([1, 2]), fromArray<number>([]));
+    const result = await collect(source);
+    expect(result).toEqual([1, 2]);
+  });
+
+  it("returns empty when all sources are empty", async () => {
+    const source = chain(fromArray<number>([]), fromArray<number>([]));
+    const result = await collect(source);
+    expect(result).toEqual([]);
+  });
+});
+
+describe("join", () => {
+  it("joins two sources on matching keys", async () => {
+    const source1 = fromArray([
+      { id: 1, name: "alice" },
+      { id: 2, name: "bob" },
+      { id: 3, name: "carol" },
+    ]);
+    const source2 = fromArray([
+      { userId: 2, role: "admin" },
+      { userId: 3, role: "user" },
+      { userId: 1, role: "user" },
+    ]);
+    const result = await collect(
+      join(
+        source1,
+        source2,
+        (v: { id: number; name: string }) => v.id,
+        (v: { userId: number; role: string }) => v.userId,
+      ),
+    );
+    expect(result).toEqual([
+      [
+        { id: 1, name: "alice" },
+        { userId: 1, role: "user" },
+      ],
+      [
+        { id: 2, name: "bob" },
+        { userId: 2, role: "admin" },
+      ],
+      [
+        { id: 3, name: "carol" },
+        { userId: 3, role: "user" },
+      ],
+    ]);
+  });
+
+  it("yields nothing when no keys match", async () => {
+    const source1 = fromArray([{ id: 1, name: "alice" }]);
+    const source2 = fromArray([{ userId: 99, role: "admin" }]);
+    const result = await collect(
+      join(
+        source1,
+        source2,
+        (v: { id: number; name: string }) => v.id,
+        (v: { userId: number; role: string }) => v.userId,
+      ),
+    );
+    expect(result).toEqual([]);
+  });
+
+  it("handles empty sources", async () => {
+    const source1 = fromArray<{ id: number; name: string }>([]);
+    const source2 = fromArray<{ userId: number; role: string }>([]);
+    const result = await collect(
+      join(source1, source2, (v) => v.id, (v) => v.userId),
+    );
+    expect(result).toEqual([]);
+  });
+
+  it("joins with duplicate keys in source2 (last wins)", async () => {
+    const source1 = fromArray([{ id: 1, name: "alice" }]);
+    const source2 = fromArray([
+      { userId: 1, role: "admin" },
+      { userId: 1, role: "user" },
+    ]);
+    const result = await collect(
+      join(
+        source1,
+        source2,
+        (v: { id: number; name: string }) => v.id,
+        (v: { userId: number; role: string }) => v.userId,
+      ),
+    );
+    expect(result).toHaveLength(1);
+    expect(result[0][0]).toEqual({ id: 1, name: "alice" });
+    expect(result[0][1].role).toBe("user");
+  });
+});
\ No newline at end of file