Add tests for the versioning model

src/jest.setup.js

@@ -1,9 +1,25 @@
 expect.extend({
+  toBeOfType(received, expectedType) {
+    const type = typeof received;
+
+    const pass = type === expectedType;
+    const message = () => `
+      Expected value to be of type ${this.utils.printExpected(expectedType)},
+      but received ${this.utils.printReceived(type)}`;
+
+    return {
+      message,
+      pass,
+    };
+  },
+
   toBeEitherAFunctionOrAnObject(received) {
     const type = typeof received;
 
     const pass = ['object', 'function'].includes(type);
-    const message = `Expected a function or an object, received ${type}`;
+    const message = () => `Expected a ${this.utils.printExpected('function')}
+      or an ${this.utils.printExpected('object')},
+      but received ${type}`;
 
     return {
       message,
@@ -11,5 +27,3 @@ expect.extend({
     };
   },
 });
-
-jest.mock('./model/input');