Configure test coverage

Author: Pytal

.gitignore

@@ -1,2 +1,3 @@
 /node_modules
 /lib
+/coverage

jest.config.js

@@ -2,4 +2,14 @@ module.exports = {
   transform: {
     '^.+\\.ts$': 'esbuild-jest',
   },
+  collectCoverage: true,
+  coverageProvider: 'babel',
+  coverageThreshold: {
+    global: {
+      branches: 100,
+      functions: 100,
+      lines: 100,
+      statements: 100,
+    },
+  },
 }