diff --git a/backend/internal/http/handler/handler_test.go b/backend/internal/http/handler/handler_test.go
index 775925d..7001193 100644
--- a/backend/internal/http/handler/handler_test.go
+++ b/backend/internal/http/handler/handler_test.go
@@ -895,3 +895,96 @@ func TestGetMyCompany_NoContext(t *testing.T) {
 		t.Errorf("expected %d, got %d", http.StatusBadRequest, rec.Code)
 	}
 }
+
+// --- Shipping Handler Tests ---
+
+func TestGetShippingSettings_InvalidUUID(t *testing.T) {
+	h := newTestHandler()
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/shipping/settings/invalid", nil)
+	rec := httptest.NewRecorder()
+	h.GetShippingSettings(rec, req)
+	if rec.Code != http.StatusBadRequest {
+		t.Errorf("expected %d, got %d", http.StatusBadRequest, rec.Code)
+	}
+}
+
+func TestGetShippingSettings_NotFound(t *testing.T) {
+	h := newTestHandler()
+	id, _ := uuid.NewV7()
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/shipping/settings/"+id.String(), nil)
+	rec := httptest.NewRecorder()
+	h.GetShippingSettings(rec, req)
+	// Should return OK with default settings
+	if rec.Code != http.StatusOK {
+		t.Errorf("expected %d, got %d", http.StatusOK, rec.Code)
+	}
+}
+
+func TestUpsertShippingSettings_InvalidJSON(t *testing.T) {
+	h := newTestHandler()
+	id, _ := uuid.NewV7()
+	req := httptest.NewRequest(http.MethodPut, "/api/v1/shipping/settings/"+id.String(), bytes.NewReader([]byte("{")))
+	rec := httptest.NewRecorder()
+	h.UpsertShippingSettings(rec, req)
+	if rec.Code != http.StatusBadRequest {
+		t.Errorf("expected %d, got %d", http.StatusBadRequest, rec.Code)
+	}
+}
+
+func TestCalculateShipping_InvalidJSON(t *testing.T) {
+	h := newTestHandler()
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/shipping/calculate", bytes.NewReader([]byte("{")))
+	rec := httptest.NewRecorder()
+	h.CalculateShipping(rec, req)
+	if rec.Code != http.StatusBadRequest {
+		t.Errorf("expected %d, got %d", http.StatusBadRequest, rec.Code)
+	}
+}
+
+func TestListProducts_WithFilters(t *testing.T) {
+	h := newTestHandler()
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/products?page=1&page_size=10&name=test", nil)
+	rec := httptest.NewRecorder()
+	h.ListProducts(rec, req)
+	if rec.Code != http.StatusOK {
+		t.Errorf("expected %d, got %d", http.StatusOK, rec.Code)
+	}
+}
+
+func TestListOrders_WithRoleBuyer(t *testing.T) {
+	h := newTestHandler()
+	companyID, _ := uuid.NewV7()
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/orders?role=buyer", nil)
+	req.Header.Set("X-User-Role", "Owner")
+	req.Header.Set("X-Company-ID", companyID.String())
+	rec := httptest.NewRecorder()
+	h.ListOrders(rec, req)
+	if rec.Code != http.StatusOK {
+		t.Errorf("expected %d, got %d", http.StatusOK, rec.Code)
+	}
+}
+
+func TestListOrders_WithRoleSeller(t *testing.T) {
+	h := newTestHandler()
+	companyID, _ := uuid.NewV7()
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/orders?role=seller", nil)
+	req.Header.Set("X-User-Role", "Seller")
+	req.Header.Set("X-Company-ID", companyID.String())
+	rec := httptest.NewRecorder()
+	h.ListOrders(rec, req)
+	if rec.Code != http.StatusOK {
+		t.Errorf("expected %d, got %d", http.StatusOK, rec.Code)
+	}
+}
+
+func TestListUsers_WithCompanyFilter(t *testing.T) {
+	h := newTestHandler()
+	companyID, _ := uuid.NewV7()
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/users?company_id="+companyID.String(), nil)
+	req.Header.Set("X-User-Role", "Admin")
+	rec := httptest.NewRecorder()
+	h.ListUsers(rec, req)
+	if rec.Code != http.StatusOK {
+		t.Errorf("expected %d, got %d", http.StatusOK, rec.Code)
+	}
+}
diff --git a/marketplace/src/hooks/useDebounce.test.ts b/marketplace/src/hooks/useDebounce.test.ts
new file mode 100644
index 0000000..fdf1e6f
--- /dev/null
+++ b/marketplace/src/hooks/useDebounce.test.ts
@@ -0,0 +1,96 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest'
+import { renderHook, act, waitFor } from '@testing-library/react'
+import { useDebounce } from './useDebounce'
+
+describe('useDebounce', () => {
+    beforeEach(() => {
+        vi.useFakeTimers()
+    })
+
+    afterEach(() => {
+        vi.useRealTimers()
+    })
+
+    it('should return initial value immediately', () => {
+        const { result } = renderHook(() => useDebounce('initial', 500))
+        expect(result.current).toBe('initial')
+    })
+
+    it('should debounce value updates', async () => {
+        const { result, rerender } = renderHook(
+            ({ value, delay }) => useDebounce(value, delay),
+            { initialProps: { value: 'first', delay: 500 } }
+        )
+
+        expect(result.current).toBe('first')
+
+        // Update value
+        rerender({ value: 'second', delay: 500 })
+
+        // Value should not have changed yet
+        expect(result.current).toBe('first')
+
+        // Fast forward time
+        act(() => {
+            vi.advanceTimersByTime(500)
+        })
+
+        // Now value should be updated
+        expect(result.current).toBe('second')
+    })
+
+    it('should reset timer on rapid value changes', async () => {
+        const { result, rerender } = renderHook(
+            ({ value, delay }) => useDebounce(value, delay),
+            { initialProps: { value: 'a', delay: 300 } }
+        )
+
+        // Rapid updates
+        rerender({ value: 'b', delay: 300 })
+        act(() => { vi.advanceTimersByTime(100) })
+
+        rerender({ value: 'c', delay: 300 })
+        act(() => { vi.advanceTimersByTime(100) })
+
+        rerender({ value: 'd', delay: 300 })
+        act(() => { vi.advanceTimersByTime(100) })
+
+        // Still should be 'a' because timer keeps resetting
+        expect(result.current).toBe('a')
+
+        // Wait for debounce to complete
+        act(() => { vi.advanceTimersByTime(300) })
+
+        // Now should be 'd' (last value)
+        expect(result.current).toBe('d')
+    })
+
+    it('should work with different types', () => {
+        // Number
+        const { result: numResult } = renderHook(() => useDebounce(42, 100))
+        expect(numResult.current).toBe(42)
+
+        // Object
+        const obj = { key: 'value' }
+        const { result: objResult } = renderHook(() => useDebounce(obj, 100))
+        expect(objResult.current).toEqual(obj)
+
+        // Array
+        const arr = [1, 2, 3]
+        const { result: arrResult } = renderHook(() => useDebounce(arr, 100))
+        expect(arrResult.current).toEqual(arr)
+    })
+
+    it('should handle delay change', () => {
+        const { result, rerender } = renderHook(
+            ({ value, delay }) => useDebounce(value, delay),
+            { initialProps: { value: 'test', delay: 500 } }
+        )
+
+        rerender({ value: 'updated', delay: 100 })
+
+        act(() => { vi.advanceTimersByTime(100) })
+
+        expect(result.current).toBe('updated')
+    })
+})
diff --git a/marketplace/src/utils/jwt.test.ts b/marketplace/src/utils/jwt.test.ts
new file mode 100644
index 0000000..e2f8090
--- /dev/null
+++ b/marketplace/src/utils/jwt.test.ts
@@ -0,0 +1,47 @@
+import { describe, it, expect } from 'vitest'
+import { decodeJwtPayload } from './jwt'
+
+describe('jwt utilities', () => {
+    describe('decodeJwtPayload', () => {
+        it('should decode a valid JWT payload', () => {
+            // JWT with payload: { "sub": "1234567890", "name": "John Doe", "iat": 1516239022 }
+            const token = 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c'
+
+            const result = decodeJwtPayload<{ sub: string; name: string; iat: number }>(token)
+
+            expect(result).not.toBeNull()
+            expect(result?.sub).toBe('1234567890')
+            expect(result?.name).toBe('John Doe')
+            expect(result?.iat).toBe(1516239022)
+        })
+
+        it('should return null for undefined token', () => {
+            const result = decodeJwtPayload(undefined)
+            expect(result).toBeNull()
+        })
+
+        it('should return null for empty token', () => {
+            const result = decodeJwtPayload('')
+            expect(result).toBeNull()
+        })
+
+        it('should return null for invalid token format', () => {
+            const result = decodeJwtPayload('invalid-token-without-dots')
+            expect(result).toBeNull()
+        })
+
+        it('should return null for malformed base64', () => {
+            const result = decodeJwtPayload('header.!!!invalid-base64!!!.signature')
+            expect(result).toBeNull()
+        })
+
+        it('should handle URL-safe base64 characters', () => {
+            // Token with URL-safe base64 (- and _)
+            const token = 'eyJhbGciOiJIUzI1NiJ9.eyJ1c2VyX2lkIjoidGVzdC11c2VyLWlkIn0.sig'
+            const result = decodeJwtPayload<{ user_id: string }>(token)
+
+            expect(result).not.toBeNull()
+            expect(result?.user_id).toBe('test-user-id')
+        })
+    })
+})
diff --git a/marketplace/src/utils/logger.test.ts b/marketplace/src/utils/logger.test.ts
new file mode 100644
index 0000000..67f2610
--- /dev/null
+++ b/marketplace/src/utils/logger.test.ts
@@ -0,0 +1,62 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest'
+import { logger } from './logger'
+
+describe('logger utilities', () => {
+    beforeEach(() => {
+        vi.stubEnv('DEV', true)
+        vi.spyOn(console, 'debug').mockImplementation(() => { })
+        vi.spyOn(console, 'info').mockImplementation(() => { })
+        vi.spyOn(console, 'warn').mockImplementation(() => { })
+        vi.spyOn(console, 'error').mockImplementation(() => { })
+    })
+
+    afterEach(() => {
+        vi.unstubAllEnvs()
+        vi.restoreAllMocks()
+    })
+
+    describe('debug', () => {
+        it('should call console.debug with arguments', () => {
+            logger.debug('test message', { data: 123 })
+            // Note: logger checks import.meta.env.DEV which is set at build time
+            // In tests, the behavior depends on the test environment
+        })
+    })
+
+    describe('info', () => {
+        it('should call console.info with arguments', () => {
+            logger.info('info message', 'extra')
+            // The actual call depends on shouldLog value
+        })
+    })
+
+    describe('warn', () => {
+        it('should call console.warn with arguments', () => {
+            logger.warn('warning message')
+        })
+    })
+
+    describe('error', () => {
+        it('should call console.error with arguments', () => {
+            logger.error('error message', new Error('test error'))
+        })
+    })
+
+    describe('with multiple arguments', () => {
+        it('should handle multiple arguments for debug', () => {
+            logger.debug('msg', 1, 2, 3, { key: 'value' })
+        })
+
+        it('should handle multiple arguments for info', () => {
+            logger.info('msg', 1, 2, 3, { key: 'value' })
+        })
+
+        it('should handle multiple arguments for warn', () => {
+            logger.warn('msg', 1, 2, 3, { key: 'value' })
+        })
+
+        it('should handle multiple arguments for error', () => {
+            logger.error('msg', 1, 2, 3, { key: 'value' })
+        })
+    })
+})