vitest setup + component tests

frontend/src/lib/api.test.ts

@@ -0,0 +1,92 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+
+describe("API client", () => {
+  const originalFetch = global.fetch;
+
+  beforeEach(() => {
+    vi.resetModules();
+  });
+
+  afterEach(() => {
+    global.fetch = originalFetch;
+  });
+
+  it("getQuestions builds correct query string with filters", async () => {
+    let capturedUrl = "";
+    global.fetch = vi.fn().mockImplementation((url: string) => {
+      capturedUrl = url;
+      return Promise.resolve({
+        ok: true,
+        json: () =>
+          Promise.resolve({
+            items: [],
+            total: 0,
+            page: 1,
+            limit: 20,
+            pages: 0,
+          }),
+      });
+    });
+
+    const { getQuestions } = await import("./api");
+    await getQuestions({ page: 2, difficulty: "easy", category: "arrays" });
+
+    expect(capturedUrl).toContain("page=2");
+    expect(capturedUrl).toContain("difficulty=easy");
+    expect(capturedUrl).toContain("category=arrays");
+  });
+
+  it("getQuestions omits empty filters", async () => {
+    let capturedUrl = "";
+    global.fetch = vi.fn().mockImplementation((url: string) => {
+      capturedUrl = url;
+      return Promise.resolve({
+        ok: true,
+        json: () =>
+          Promise.resolve({
+            items: [],
+            total: 0,
+            page: 1,
+            limit: 20,
+            pages: 0,
+          }),
+      });
+    });
+
+    const { getQuestions } = await import("./api");
+    await getQuestions({});
+
+    expect(capturedUrl).not.toContain("?");
+  });
+
+  it("throws error on non-ok response", async () => {
+    global.fetch = vi.fn().mockResolvedValue({
+      ok: false,
+      status: 404,
+      statusText: "Not Found",
+    });
+
+    const { getQuestion } = await import("./api");
+
+    await expect(getQuestion("nonexistent")).rejects.toThrow("API error: 404");
+  });
+
+  it("getStats returns stats data", async () => {
+    const mockStats = {
+      total_questions: 10,
+      by_difficulty: { easy: 3, medium: 5, hard: 2 },
+      by_category: [],
+      by_pattern: [],
+    };
+
+    global.fetch = vi.fn().mockResolvedValue({
+      ok: true,
+      json: () => Promise.resolve(mockStats),
+    });
+
+    const { getStats } = await import("./api");
+    const result = await getStats();
+
+    expect(result).toEqual(mockStats);
+  });
+});