diff --git a/frontend/testing/unit/api.request-behavior.test.ts b/frontend/testing/unit/api.request-behavior.test.ts
new file mode 100644
index 00000000..4437ff65
--- /dev/null
+++ b/frontend/testing/unit/api.request-behavior.test.ts
@@ -0,0 +1,160 @@
+/**
+ * Frontend API request behavior tests.
+ *
+ * Covers:
+ * - Successful JSON responses
+ * - Non-OK HTTP responses
+ * - Timeout + abort behavior
+ * - Timeout cleanup
+ */
+
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import { getHealth, listPlugins } from '../../src/api'
+
+// -----------------------------------------------------------------------------
+// Helpers
+// -----------------------------------------------------------------------------
+
+function mockJsonResponse(status: number, body: unknown = {}) {
+  return Promise.resolve({
+    ok: status >= 200 && status < 300,
+    status,
+    json: () => Promise.resolve(body),
+  } as Response)
+}
+
+// -----------------------------------------------------------------------------
+// Shared cleanup
+// -----------------------------------------------------------------------------
+
+afterEach(() => {
+  vi.useRealTimers()
+  vi.restoreAllMocks()
+  vi.unstubAllGlobals()
+})
+
+// -----------------------------------------------------------------------------
+// Successful responses
+// -----------------------------------------------------------------------------
+
+describe('API request — successful responses', () => {
+  it('successfully parses JSON response', async () => {
+    const responseBody = {
+      plugins: [{ id: 'nmap', name: 'Nmap' }],
+      total: 1,
+    }
+
+    vi.stubGlobal(
+      'fetch',
+      vi.fn().mockReturnValue(mockJsonResponse(200, responseBody)),
+    )
+
+    const result = await listPlugins()
+
+    expect(result).toEqual(responseBody)
+  })
+
+  it('clears timeout after successful response', async () => {
+    const clearTimeoutSpy = vi.spyOn(window, 'clearTimeout')
+
+    vi.stubGlobal(
+      'fetch',
+      vi.fn().mockReturnValue(mockJsonResponse(200, { ok: true })),
+    )
+
+    await getHealth()
+
+    expect(clearTimeoutSpy).toHaveBeenCalled()
+  })
+})
+
+// -----------------------------------------------------------------------------
+// Non-OK HTTP responses
+// -----------------------------------------------------------------------------
+
+describe('API request — non-OK responses', () => {
+  it('throws on non-OK HTTP response', async () => {
+    vi.stubGlobal(
+      'fetch',
+      vi.fn().mockReturnValue(mockJsonResponse(500)),
+    )
+
+    await expect(getHealth()).rejects.toThrow('Request failed: 500')
+  })
+})
+
+// -----------------------------------------------------------------------------
+// Timeout + abort behavior
+// -----------------------------------------------------------------------------
+
+describe('API request — timeout behavior', () => {
+  it('sets a 10-second timeout', async () => {
+    const setTimeoutSpy = vi.spyOn(window, 'setTimeout')
+
+    vi.stubGlobal(
+      'fetch',
+      vi.fn().mockReturnValue(mockJsonResponse(200, {})),
+    )
+
+    await getHealth()
+
+    expect(setTimeoutSpy).toHaveBeenCalledWith(
+      expect.any(Function),
+      10000,
+    )
+  })
+
+  it('passes AbortSignal to fetch', async () => {
+    const fetchSpy = vi
+      .fn()
+      .mockReturnValue(mockJsonResponse(200, {}))
+
+    vi.stubGlobal('fetch', fetchSpy)
+
+    await getHealth()
+
+    const [, init] = fetchSpy.mock.calls[0]
+
+    expect(init?.signal).toBeInstanceOf(AbortSignal)
+  })
+
+  it('aborts request when timeout expires', async () => {
+    vi.useFakeTimers()
+
+    const fetchSpy = vi.fn().mockImplementation((_, init) => {
+      const signal = (init as RequestInit)?.signal
+
+      return new Promise((_, reject) => {
+        signal?.addEventListener('abort', () => {
+          reject(new DOMException('Aborted', 'AbortError'))
+        })
+      })
+    })
+
+    vi.stubGlobal('fetch', fetchSpy)
+
+    const promise = getHealth()
+
+    vi.runAllTimers()
+
+    await expect(promise).rejects.toThrow('Aborted')
+  })
+
+  it('cleans up timeout on fetch rejection', async () => {
+    vi.useFakeTimers()
+
+    const setTimeoutSpy = vi.spyOn(window, 'setTimeout')
+    const clearTimeoutSpy = vi.spyOn(window, 'clearTimeout')
+
+    vi.stubGlobal(
+      'fetch',
+      vi.fn().mockRejectedValue(new Error('Network error')),
+    )
+
+    await getHealth().catch(() => {})
+
+    const timeoutId = setTimeoutSpy.mock.results[0].value
+
+    expect(clearTimeoutSpy).toHaveBeenCalledWith(timeoutId)
+  })
+})
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