feat: improved calculator

jest.config.js

@@ -0,0 +1,17 @@
+export default {
+  preset: 'ts-jest',
+  testEnvironment: 'node',
+  roots: ['<rootDir>/src'],
+  testMatch: [
+    '**/__tests__/**/*.ts',
+    '**/?(*.)+(spec|test).ts'
+  ],
+  transform: {
+    '^.+\\.ts$': 'ts-jest',
+  },
+  moduleFileExtensions: ['ts', 'js', 'json'],
+  collectCoverageFrom: [
+    'src/**/*.ts',
+    '!src/**/*.d.ts',
+  ],
+};