1 files changed, 58 insertions, 0 deletions
diff --git a/web/test/budget.test.mjs b/web/test/budget.test.mjs
new file mode 100644
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+++ b/web/test/budget.test.mjs
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+// budget.test.mjs — Unit tests for budget headroom display.
+//
+// Run with: node --test web/test/budget.test.mjs
+
+import { describe, it } from 'node:test';
+import assert from 'node:assert/strict';
+import { formatBudgetHeadroom, renderBudgetHeadroom } from '../app.js';
+
+function makeDoc() {
+  return {
+    createElement(tag) {
+      return {
+        tag,
+        className: '',
+        textContent: '',
+        children: [],
+        appendChild(child) { this.children.push(child); return child; },
+      };
+    },
+  };
+}
+
+describe('formatBudgetHeadroom', () => {
+  it('formats a limited provider with percent and dollars', () => {
+    assert.equal(
+      formatBudgetHeadroom({ provider: 'claude', limited: true, limit_usd: 10, remaining_usd: 6, fraction_remaining: 0.6 }),
+      'Claude: 60% left ($6.00 of $10.00)',
+    );
+  });
+
+  it('returns empty string for unlimited providers', () => {
+    assert.equal(formatBudgetHeadroom({ provider: 'local', limited: false }), '');
+    assert.equal(formatBudgetHeadroom(null), '');
+  });
+});
+
+describe('renderBudgetHeadroom', () => {
+  it('renders one chip per limited provider, skipping unlimited', () => {
+    const wrap = renderBudgetHeadroom([
+      { provider: 'claude', limited: true, limit_usd: 10, remaining_usd: 6, fraction_remaining: 0.6 },
+      { provider: 'local', limited: false },
+    ], makeDoc());
+    assert.equal(wrap.children.length, 1);
+    assert.equal(wrap.children[0].className, 'budget-chip');
+    assert.match(wrap.children[0].textContent, /Claude: 60% left/);
+  });
+
+  it('flags providers under 20% remaining with --low', () => {
+    const wrap = renderBudgetHeadroom([
+      { provider: 'gemini', limited: true, limit_usd: 5, remaining_usd: 0.5, fraction_remaining: 0.1 },
+    ], makeDoc());
+    assert.equal(wrap.children[0].className, 'budget-chip budget-chip--low');
+  });
+
+  it('returns null when doc is null', () => {
+    assert.equal(renderBudgetHeadroom([], null), null);
+  });
+});