test: add zero-signer edge case test to ThresholdConfig quorum preview

frontend/src/components/ThresholdConfig/ThresholdConfig.test.tsx

@@ -0,0 +1,146 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest'
+import '@testing-library/jest-dom'
+import { render, screen, fireEvent, waitFor } from '@testing-library/react'
+import ThresholdConfig from './ThresholdConfig'
+
+// ---------------------------------------------------------------------------
+// Fetch mock helpers
+// ---------------------------------------------------------------------------
+
+type FetchRoute = {
+  url: RegExp | string
+  response: unknown
+  status?: number
+}
+
+function setupFetch(routes: FetchRoute[]) {
+  vi.stubGlobal(
+    'fetch',
+    vi.fn((url: string) => {
+      const route = routes.find(r =>
+        typeof r.url === 'string' ? url.includes(r.url) : r.url.test(url),
+      )
+      const status = route?.status ?? 200
+      const body = route ? JSON.stringify(route.response) : '{}'
+      return Promise.resolve({
+        ok: status >= 200 && status < 300,
+        status,
+        json: () => Promise.resolve(route?.response ?? {}),
+        text: () => Promise.resolve(body),
+      })
+    }),
+  )
+}
+
+// ---------------------------------------------------------------------------
+// Tests
+// ---------------------------------------------------------------------------
+
+describe('ThresholdConfig — zero-signer edge case (issue #235)', () => {
+  afterEach(() => {
+    vi.unstubAllGlobals()
+    vi.restoreAllMocks()
+  })
+
+  it('shows a placeholder warning instead of a broken/empty quorum preview when signers list is empty', async () => {
+    setupFetch([
+      { url: /threshold/, response: { threshold: 2 } },
+      { url: /signers/, response: [] },         // ← zero signers
+    ])
+
+    render(<ThresholdConfig />)
+
+    // Wait for the component to finish loading
+    await waitFor(() => {
+      expect(screen.queryByText(/Loading current value/i)).not.toBeInTheDocument()
+    })
+
+    // Enter a valid threshold value so quorum preview section becomes visible
+    const input = screen.getByLabelText(/new threshold/i)
+    fireEvent.change(input, { target: { value: '3' } })
+
+    // The quorum preview section should appear with an informative message
+    await waitFor(() => {
+      expect(screen.getByText(/No signers registered/i)).toBeInTheDocument()
+    })
+  })
+
+  it('does NOT show a NaN or divide-by-zero value when signers list is empty', async () => {
+    setupFetch([
+      { url: /threshold/, response: { threshold: 5 } },
+      { url: /signers/, response: [] },
+    ])
+
+    render(<ThresholdConfig />)
+
+    await waitFor(() => {
+      expect(screen.queryByText(/Loading current value/i)).not.toBeInTheDocument()
+    })
+
+    const input = screen.getByLabelText(/new threshold/i)
+    fireEvent.change(input, { target: { value: '5' } })
+
+    // Allow any async state settling
+    await waitFor(() => {
+      const bodyText = document.body.textContent ?? ''
+      expect(bodyText).not.toMatch(/NaN/)
+      expect(bodyText).not.toMatch(/Infinity/)
+      expect(bodyText).not.toMatch(/undefined/)
+    })
+  })
+
+  it('shows quorum preview normally when signers are present', async () => {
+    setupFetch([
+      { url: /threshold/, response: { threshold: 2 } },
+      {
+        url: /signers/,
+        response: [
+          { address: 'GAAZI4TCR3TY5OJHCTJC2A4QSY6CJWJH5IAJTGKIN2ER7LBNVKOCCWN', weight: 2 },
+          { address: 'GBVVJJPJZ3GR4VZVKNL4EOXTMQBQUXOUMGJXHWLZAGNNPPLZEXFQBVF', weight: 1 },
+        ],
+      },
+    ])
+
+    render(<ThresholdConfig />)
+
+    await waitFor(() => {
+      expect(screen.queryByText(/Loading current value/i)).not.toBeInTheDocument()
+    })
+
+    const input = screen.getByLabelText(/new threshold/i)
+    fireEvent.change(input, { target: { value: '2' } })
+
+    await waitFor(() => {
+      expect(screen.getByText(/Quorum Preview/i)).toBeInTheDocument()
+      expect(screen.getByText(/Required signers:/i)).toBeInTheDocument()
+    })
+
+    // No "no signers" warning when signers are actually present
+    expect(screen.queryByText(/No signers registered/i)).not.toBeInTheDocument()
+  })
+
+  it('shows infeasible threshold warning when threshold exceeds total signer weight', async () => {
+    setupFetch([
+      { url: /threshold/, response: { threshold: 1 } },
+      {
+        url: /signers/,
+        response: [
+          { address: 'GAAZI4TCR3TY5OJHCTJC2A4QSY6CJWJH5IAJTGKIN2ER7LBNVKOCCWN', weight: 1 },
+        ],
+      },
+    ])
+
+    render(<ThresholdConfig />)
+
+    await waitFor(() => {
+      expect(screen.queryByText(/Loading current value/i)).not.toBeInTheDocument()
+    })
+
+    const input = screen.getByLabelText(/new threshold/i)
+    fireEvent.change(input, { target: { value: '999' } })
+
+    await waitFor(() => {
+      expect(screen.getByText(/unreachable/i)).toBeInTheDocument()
+    })
+  })
+})

frontend/src/components/ThresholdConfig/ThresholdConfig.tsx

@@ -167,6 +167,17 @@ export default function ThresholdConfig() {
           </p>
         )}
 
+        {/* Zero-signer edge case: show a clear placeholder instead of silently
+            rendering nothing, which could look like a loading or broken state. */}
+        {isValid && !signersLoading && signers.length === 0 && (
+          <div className="threshold-quorum-preview threshold-quorum-preview--empty">
+            <h4 className="threshold-quorum-preview__title">Quorum Preview</h4>
+            <p className="threshold-quorum-preview__warning">
+              ⚠️ No signers registered. Add signers before configuring a threshold.
+            </p>
+          </div>
+        )}
+
         {quorumPreview && (
           <div className="threshold-quorum-preview">
             <h4 className="threshold-quorum-preview__title">Quorum Preview</h4>