diff --git a/CHANGELOG.md b/CHANGELOG.md
index a389c0c5..4dfc5baf 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,7 @@ and this project adheres to
 ## Changed
 
 - 📝(frontend) Update documentation
+- ✅(frontend) Improve tests coverage
 
 ## [3.2.1] - 2025-05-06
 
diff --git a/src/frontend/apps/impress/src/api/__tests__/APIError.test.ts b/src/frontend/apps/impress/src/api/__tests__/APIError.test.ts
new file mode 100644
index 00000000..395a5460
--- /dev/null
+++ b/src/frontend/apps/impress/src/api/__tests__/APIError.test.ts
@@ -0,0 +1,36 @@
+import { APIError, isAPIError } from '@/api';
+
+describe('APIError', () => {
+  it('should correctly instantiate with required fields', () => {
+    const error = new APIError('Something went wrong', { status: 500 });
+
+    expect(error).toBeInstanceOf(Error);
+    expect(error).toBeInstanceOf(APIError);
+    expect(error.message).toBe('Something went wrong');
+    expect(error.status).toBe(500);
+    expect(error.cause).toBeUndefined();
+    expect(error.data).toBeUndefined();
+  });
+
+  it('should correctly instantiate with all fields', () => {
+    const details = { field: 'email' };
+    const error = new APIError('Validation failed', {
+      status: 400,
+      cause: ['Invalid email format'],
+      data: details,
+    });
+
+    expect(error.name).toBe('APIError');
+    expect(error.status).toBe(400);
+    expect(error.cause).toEqual(['Invalid email format']);
+    expect(error.data).toEqual(details);
+  });
+
+  it('should be detected by isAPIError type guard', () => {
+    const error = new APIError('Unauthorized', { status: 401 });
+    const notAnError = { message: 'Fake error' };
+
+    expect(isAPIError(error)).toBe(true);
+    expect(isAPIError(notAnError)).toBe(false);
+  });
+});
diff --git a/src/frontend/apps/impress/src/api/__tests__/config.test.ts b/src/frontend/apps/impress/src/api/__tests__/config.test.ts
new file mode 100644
index 00000000..cb9bf268
--- /dev/null
+++ b/src/frontend/apps/impress/src/api/__tests__/config.test.ts
@@ -0,0 +1,16 @@
+import { baseApiUrl } from '@/api';
+
+describe('config', () => {
+  it('constructs URL with default version', () => {
+    expect(baseApiUrl()).toBe('http://test.jest/api/v1.0/');
+  });
+
+  it('constructs URL with custom version', () => {
+    expect(baseApiUrl('2.0')).toBe('http://test.jest/api/v2.0/');
+  });
+
+  it('uses env origin if available', () => {
+    process.env.NEXT_PUBLIC_API_ORIGIN = 'https://env.example.com';
+    expect(baseApiUrl('3.0')).toBe('https://env.example.com/api/v3.0/');
+  });
+});
diff --git a/src/frontend/apps/impress/src/api/__tests__/fetchApi.test.tsx b/src/frontend/apps/impress/src/api/__tests__/fetchApi.test.tsx
index 05dc0b13..9b9d6a9a 100644
--- a/src/frontend/apps/impress/src/api/__tests__/fetchApi.test.tsx
+++ b/src/frontend/apps/impress/src/api/__tests__/fetchApi.test.tsx
@@ -36,4 +36,13 @@ describe('fetchAPI', () => {
 
     expect(fetchMock.lastUrl()).toEqual('http://test.jest/api/v2.0/some/url');
   });
+
+  it('removes Content-Type header when withoutContentType is true', async () => {
+    fetchMock.mock('http://test.jest/api/v1.0/some/url', 200);
+
+    await fetchAPI('some/url', { withoutContentType: true });
+
+    const options = fetchMock.lastOptions();
+    expect(options?.headers).not.toHaveProperty('Content-Type');
+  });
 });
diff --git a/src/frontend/apps/impress/src/api/__tests__/helpers.test.tsx b/src/frontend/apps/impress/src/api/__tests__/helpers.test.tsx
new file mode 100644
index 00000000..e4706367
--- /dev/null
+++ b/src/frontend/apps/impress/src/api/__tests__/helpers.test.tsx
@@ -0,0 +1,59 @@
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
+import { renderHook, waitFor } from '@testing-library/react';
+
+import { useAPIInfiniteQuery } from '@/api';
+
+interface DummyItem {
+  id: number;
+}
+
+interface DummyResponse {
+  results: DummyItem[];
+  next?: string;
+}
+
+const createWrapper = () => {
+  const queryClient = new QueryClient();
+  return ({ children }: { children: React.ReactNode }) => (
+    <QueryClientProvider client={queryClient}>{children}</QueryClientProvider>
+  );
+};
+
+describe('helpers', () => {
+  it('fetches and paginates correctly', async () => {
+    const mockAPI = jest
+      .fn<Promise<DummyResponse>, [{ page: number; query: string }]>()
+      .mockResolvedValueOnce({
+        results: [{ id: 1 }],
+        next: 'url?page=2',
+      })
+      .mockResolvedValueOnce({
+        results: [{ id: 2 }],
+        next: undefined,
+      });
+
+    const { result } = renderHook(
+      () => useAPIInfiniteQuery('test-key', mockAPI, { query: 'test' }),
+      { wrapper: createWrapper() },
+    );
+
+    // Wait for first page
+    await waitFor(() => {
+      expect(result.current.data?.pages[0].results[0].id).toBe(1);
+    });
+
+    // Fetch next page
+    await result.current.fetchNextPage();
+
+    await waitFor(() => {
+      expect(result.current.data?.pages.length).toBe(2);
+    });
+
+    await waitFor(() => {
+      expect(result.current.data?.pages[1].results[0].id).toBe(2);
+    });
+
+    expect(mockAPI).toHaveBeenCalledWith({ query: 'test', page: 1 });
+    expect(mockAPI).toHaveBeenCalledWith({ query: 'test', page: 2 });
+  });
+});
diff --git a/src/frontend/apps/impress/src/api/__tests__/utils.test.ts b/src/frontend/apps/impress/src/api/__tests__/utils.test.ts
new file mode 100644
index 00000000..86433188
--- /dev/null
+++ b/src/frontend/apps/impress/src/api/__tests__/utils.test.ts
@@ -0,0 +1,57 @@
+import { errorCauses, getCSRFToken } from '@/api';
+
+describe('utils', () => {
+  describe('errorCauses', () => {
+    const createMockResponse = (jsonData: any, status = 400): Response => {
+      return {
+        status,
+        json: () => jsonData,
+      } as unknown as Response;
+    };
+
+    it('parses multiple string causes from error body', async () => {
+      const mockResponse = createMockResponse(
+        {
+          field: ['error message 1', 'error message 2'],
+        },
+        400,
+      );
+
+      const result = await errorCauses(mockResponse, { context: 'login' });
+
+      expect(result.status).toBe(400);
+      expect(result.cause).toEqual(['error message 1', 'error message 2']);
+      expect(result.data).toEqual({ context: 'login' });
+    });
+
+    it('returns undefined causes if no JSON body', async () => {
+      const mockResponse = createMockResponse(null, 500);
+
+      const result = await errorCauses(mockResponse);
+
+      expect(result.status).toBe(500);
+      expect(result.cause).toBeUndefined();
+      expect(result.data).toBeUndefined();
+    });
+  });
+
+  describe('getCSRFToken', () => {
+    it('extracts csrftoken from document.cookie', () => {
+      Object.defineProperty(document, 'cookie', {
+        writable: true,
+        value: 'sessionid=xyz; csrftoken=abc123; theme=dark',
+      });
+
+      expect(getCSRFToken()).toBe('abc123');
+    });
+
+    it('returns undefined if csrftoken is not present', () => {
+      Object.defineProperty(document, 'cookie', {
+        writable: true,
+        value: 'sessionid=xyz; theme=dark',
+      });
+
+      expect(getCSRFToken()).toBeUndefined();
+    });
+  });
+});