diff --git a/code/websites/pokedex.online/tests/unit/composables/useChallongeClient.test.js b/code/websites/pokedex.online/tests/unit/composables/useChallongeClient.test.js
new file mode 100644
index 0000000..e32a8a1
--- /dev/null
+++ b/code/websites/pokedex.online/tests/unit/composables/useChallongeClient.test.js
@@ -0,0 +1,126 @@
+/**
+ * useChallongeClient Composable Tests
+ */
+
+import { describe, it, expect, vi } from 'vitest';
+import { ref } from 'vue';
+import { ScopeType } from '../../../src/services/challonge.service.js';
+
+// Mock dependencies before importing composable
+vi.mock('../../../src/composables/useChallongeApiKey.js', () => ({
+  useChallongeApiKey: () => ({
+    getApiKey: () => 'test-api-key-1234567890'
+  })
+}));
+
+vi.mock('../../../src/composables/useChallongeOAuth.js', () => ({
+  useChallongeOAuth: () => ({
+    isAuthenticated: ref(false),
+    accessToken: ref(null)
+  })
+}));
+
+vi.mock('../../../src/composables/useChallongeClientCredentials.js', () => ({
+  useChallongeClientCredentials: () => ({
+    isAuthenticated: ref(false),
+    accessToken: ref(null)
+  })
+}));
+
+vi.mock('../../../src/services/challonge.service.js', async () => {
+  const actual = await vi.importActual('../../../src/services/challonge.service.js');
+  return {
+    ...actual,
+    createChallongeV1Client: vi.fn(() => ({ version: 'v1', mock: true })),
+    createChallongeV2Client: vi.fn(() => ({ version: 'v2.1', mock: true }))
+  };
+});
+
+import { useChallongeClient } from '../../../src/composables/useChallongeClient.js';
+
+describe('useChallongeClient', () => {
+  it('creates composable with default values', () => {
+    const {
+      apiVersion,
+      tournamentScope,
+      debugMode
+    } = useChallongeClient();
+
+    expect(apiVersion.value).toBe('v2.1');
+    expect(tournamentScope.value).toBe(ScopeType.USER);
+    expect(debugMode.value).toBe(false);
+  });
+
+  it('creates client successfully', () => {
+    const { client } = useChallongeClient();
+    
+    expect(client.value).toBeDefined();
+    expect(client.value).toHaveProperty('version');
+  });
+
+  it('switches API version', () => {
+    const { apiVersion, switchVersion } = useChallongeClient();
+
+    expect(apiVersion.value).toBe('v2.1');
+
+    switchVersion('v1');
+
+    expect(apiVersion.value).toBe('v1');
+  });
+
+  it('throws error for invalid API version', () => {
+    const { switchVersion } = useChallongeClient();
+
+    expect(() => switchVersion('v3')).toThrow('Invalid API version');
+  });
+
+  it('changes tournament scope', () => {
+    const { tournamentScope, setScope } = useChallongeClient();
+
+    expect(tournamentScope.value).toBe(ScopeType.USER);
+
+    setScope(ScopeType.APPLICATION);
+
+    expect(tournamentScope.value).toBe(ScopeType.APPLICATION);
+  });
+
+  it('throws error for invalid scope', () => {
+    const { setScope } = useChallongeClient();
+
+    expect(() => setScope('invalid')).toThrow('Invalid scope type');
+  });
+
+  it('masks API key correctly', () => {
+    const { maskedApiKey } = useChallongeClient();
+
+    const masked = maskedApiKey.value;
+    expect(masked).toContain('•••');
+    expect(masked.startsWith('test')).toBe(true);
+    expect(masked.endsWith('7890')).toBe(true);
+  });
+
+  it('returns auth type', () => {
+    const { authType } = useChallongeClient();
+
+    expect(authType.value).toBe('API Key');
+  });
+
+  it('toggles debug mode', () => {
+    const { debugMode, setDebugMode } = useChallongeClient();
+
+    expect(debugMode.value).toBe(false);
+
+    setDebugMode(true);
+
+    expect(debugMode.value).toBe(true);
+  });
+
+  it('exposes constants', () => {
+    const { ScopeType: ST, AuthType: AT } = useChallongeClient();
+
+    expect(ST).toBeDefined();
+    expect(AT).toBeDefined();
+    expect(ST.USER).toBe('user');
+    expect(ST.APPLICATION).toBe('application');
+  });
+});