Moving Jest setup and consolidating

src/components/Header/test.js

@@ -3,18 +3,9 @@ import { shallow } from 'enzyme';
 
 import { Header } from 'components/Header';
 
-const env = { ...process.env };
-
 describe('Header', () => {
-  afterEach(() => {
-    process.env = env;
-  });
-
   beforeEach(() => {
-    process.env = {
-      ...process.env,
-      BANNER: 'testing'
-    };
+    process.env.BANNER = 'testing';
   });
 
   test('rendering', () => {

src/setup-jest.js

@@ -1,4 +0,0 @@
-import Enzyme from 'enzyme';
-import Adapter from 'enzyme-adapter-react-16';
-
-Enzyme.configure({ adapter: new Adapter() });

src/setup/jest.js

@@ -0,0 +1,16 @@
+import Enzyme from 'enzyme';
+import Adapter from 'enzyme-adapter-react-16';
+
+Enzyme.configure({ adapter: new Adapter() });
+
+const env = { ...process.env };
+
+beforeEach(() => {
+  process.env = {
+    ...process.env
+  };
+});
+
+afterEach(() => {
+  process.env = env;
+});