diff --git a/src/components/__tests__/ProfileCard.test.tsx b/src/components/__tests__/ProfileCard.test.tsx
new file mode 100644
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+++ b/src/components/__tests__/ProfileCard.test.tsx
@@ -0,0 +1,123 @@
+// @vitest-environment jsdom
+import { describe, it, expect } from "vitest";
+import { render, screen } from "@testing-library/react";
+import "@testing-library/jest-dom";
+import ProfileCard from "../ProfileCard";
+import type { UserProfile } from "@/lib/types";
+
+const mockProfile: UserProfile = {
+  login: "octocat",
+  avatar_url: "https://github.com/images/error/octocat_happy.gif",
+  name: "The Octocat",
+  bio: "I'm a GitHub mascot.",
+  company: "@github",
+  location: "San Francisco",
+  blog: "https://github.blog",
+  twitter_username: "github",
+  created_at: "2011-01-25T18:44:36Z",
+  followers: 1000,
+  following: 50,
+  public_repos: 100,
+  orgs: [
+    { login: "github", avatar_url: "https://avatars.githubusercontent.com/u/9919?v=4" }
+  ],
+  pinnedRepos: [
+    {
+      name: "Spoon-Knife",
+      description: "This repo is for demonstration purposes only.",
+      url: "https://github.com/octocat/Spoon-Knife",
+      stargazerCount: 15000,
+      primaryLanguage: { name: "HTML", color: "#e34c26" }
+    }
+  ]
+};
+
+describe("ProfileCard", () => {
+  it("renders basic profile information correctly", () => {
+    render(<ProfileCard profile={mockProfile} />);
+
+    // Name and login
+    expect(screen.getByText("The Octocat")).toBeInTheDocument();
+    expect(screen.getByText("@octocat")).toBeInTheDocument();
+
+    // Stats
+    expect(screen.getByText(mockProfile.followers.toLocaleString())).toBeInTheDocument();
+    expect(screen.getByText(mockProfile.following.toLocaleString())).toBeInTheDocument();
+    expect(screen.getByText(mockProfile.public_repos.toLocaleString())).toBeInTheDocument();
+
+    // Join date - "Joined January 2011"
+    expect(screen.getByText(/Joined January 2011/)).toBeInTheDocument();
+  });
+
+  it("falls back to login when name is null", () => {
+    const profileWithoutName = { ...mockProfile, name: null };
+    render(<ProfileCard profile={profileWithoutName} />);
+
+    expect(screen.getByRole("heading", { level: 2, name: "octocat" })).toBeInTheDocument();
+    expect(screen.getByText("@octocat")).toBeInTheDocument();
+  });
+
+  it("renders optional fields when provided", () => {
+    render(<ProfileCard profile={mockProfile} />);
+
+    expect(screen.getByText("I'm a GitHub mascot.")).toBeInTheDocument();
+    expect(screen.getByText("@github")).toBeInTheDocument();
+    expect(screen.getByText("San Francisco")).toBeInTheDocument();
+    expect(screen.getByText("github.blog")).toBeInTheDocument();
+  });
+
+  it("does not render optional fields when null", () => {
+    const minimalProfile = {
+      ...mockProfile,
+      bio: null,
+      company: null,
+      location: null,
+      blog: null,
+      orgs: [],
+      pinnedRepos: []
+    };
+    render(<ProfileCard profile={minimalProfile} />);
+
+    expect(screen.queryByText("I'm a GitHub mascot.")).not.toBeInTheDocument();
+    expect(screen.queryByText("@github")).not.toBeInTheDocument();
+    expect(screen.queryByText("San Francisco")).not.toBeInTheDocument();
+    expect(screen.queryByText("github.blog")).not.toBeInTheDocument();
+    expect(screen.queryByText("Organizations")).not.toBeInTheDocument();
+    expect(screen.queryByText("Pinned Repositories")).not.toBeInTheDocument();
+  });
+
+  it("renders organizations correctly", () => {
+    render(<ProfileCard profile={mockProfile} />);
+    screen.getByText("Organizations");
+    screen.getByText("github");
+  });
+
+  it("renders pinned repositories correctly", () => {
+    render(<ProfileCard profile={mockProfile} />);
+    expect(screen.getByText("Pinned Repositories")).toBeInTheDocument();
+    expect(screen.getByText("Spoon-Knife")).toBeInTheDocument();
+    expect(screen.getByText("This repo is for demonstration purposes only.")).toBeInTheDocument();
+    expect(screen.getByText("HTML")).toBeInTheDocument();
+    expect(screen.getByText(mockProfile.pinnedRepos[0].stargazerCount.toLocaleString())).toBeInTheDocument();
+  });
+
+  it("handles pinned repos without description or language", () => {
+    const profileWithMinimalRepo = {
+      ...mockProfile,
+      pinnedRepos: [
+        {
+          name: "Empty-Repo",
+          description: null,
+          url: "https://github.com/octocat/Empty-Repo",
+          stargazerCount: 0,
+          primaryLanguage: null
+        }
+      ]
+    };
+    render(<ProfileCard profile={profileWithMinimalRepo} />);
+
+    expect(screen.getByText("Pinned Repositories")).toBeInTheDocument();
+    expect(screen.getByText("Empty-Repo")).toBeInTheDocument();
+    expect(screen.getByText("0")).toBeInTheDocument();
+  });
+});