refactor: organize backend by business responsibility

src/integrations/tbank/decimal.spec.ts

@@ -0,0 +1,23 @@
+import { add, formatDecimal, multiply, subtract } from '../../common/decimal';
+import { decimal } from './decimal';
+
+describe('decimal', () => {
+  it('keeps signed nanos exact without floats', () => {
+    expect(formatDecimal(decimal({ units: 0, nano: -500000000 }))).toBe('-0.5');
+    expect(
+      formatDecimal(
+        add(decimal({ units: '9007199254740993' }), decimal({ nano: 1 })),
+      ),
+    ).toBe('9007199254740993.000000001');
+    expect(
+      formatDecimal(
+        subtract(decimal({ units: 1 }), decimal({ nano: 500000000 })),
+      ),
+    ).toBe('0.5');
+    expect(
+      formatDecimal(
+        multiply(decimal({ units: 2 }), decimal({ nano: 500000000 })),
+      ),
+    ).toBe('1');
+  });
+});