test: add decorator utils test

src/decorators/__tests__/utils.test.ts

@@ -0,0 +1,27 @@
+import 'jest';
+import 'reflect-metadata';
+import { resolveType } from '../utils';
+import { GraphQLString } from 'graphql';
+import Field from '../Field';
+import { Wrapper } from '../../wrappers/Wrapper';
+
+class Foo {
+  @Field()
+  a: string = 'a';
+
+  @Field()
+  b = 'b';
+}
+
+describe('utils', () => {
+  describe('resolveType', () => {
+    it('should resolve type through reflection if not supplied', () => {
+      const type = resolveType(undefined, Foo.prototype, 'a');
+      expect((type as Wrapper<any, any>).graphQLType).toEqual(GraphQLString);
+    });
+
+    it('should throw error if type not available', () => {
+      expect(() => resolveType(undefined, Foo.prototype, 'b')).toThrow();
+    });
+  });
+});