Initial import of zappier-edge from zapier monorepo

tests/stripe.test.ts

@@ -0,0 +1,39 @@
+import { MeterEventClient, reportUsage, METER_EVENT_NAME } from '../src/billing/stripe';
+import { UsageEntry } from '../src/usage';
+
+const entry = (cents: number): UsageEntry => ({
+  customerId: 'cust_1',
+  endpointId: 'storage',
+  cents,
+  metadataBytes: 0,
+  attachmentBytes: 0,
+  timestamp: new Date(),
+});
+
+const fakeClient = () => {
+  const calls: { eventName: string; customerId: string; value: string }[] = [];
+  const client: MeterEventClient = {
+    createMeterEvent: async (params) => {
+      calls.push(params);
+    },
+  };
+  return { client, calls };
+};
+
+describe('reportUsage', () => {
+  it('reports usage minus the monthly credit as one meter event', async () => {
+    const { client, calls } = fakeClient();
+    const reported = await reportUsage(client, 'cus_123', [entry(112), entry(4)], 100);
+    expect(reported).toBe(16); // 116 - 100 credit
+    expect(calls).toEqual([
+      { eventName: METER_EVENT_NAME, customerId: 'cus_123', value: '16' },
+    ]);
+  });
+
+  it('reports nothing when the credit covers all usage', async () => {
+    const { client, calls } = fakeClient();
+    const reported = await reportUsage(client, 'cus_123', [entry(4)], 100);
+    expect(reported).toBe(0);
+    expect(calls).toHaveLength(0);
+  });
+});