add to test style guide

Author: ArcAnya

docs/style guide.md

@@ -1,14 +1,20 @@
 For testing: 
-- try to use .toMatchSnapshot() when possible. Note that it will NOT be possible to make use of .toMatchSnapshot for the component as a whole if 'useContext' is used within the component.
-- if some of the child components of the tested component uses 'useContext' then you should use ShallowRenderer from 'react-test-renderer/shallow' as follows in order to limit the Snapshot to the component itself:
+- try to use .toMatchSnapshot() when possible / relevant. Using asFragment will help bypass issues with useContext:
+```jsx
+  it('should match DOM and render "Weight per Tier (%)", "1st place winner" etc. if bounty type is 2', () => {
+    const { asFragment } = render(<SetTierAdminPage bounty={Constants.bounty2} />);
+    expect(asFragment()).toMatchSnapshot();
+```
+- to shallow render and use .toMatchSnapshot() (i.e. limit the test to the component itself) you can do:
 ```jsx 
+import ShallowRenderer from 'react-test-renderer/shallow';
 it('should render match DOM Snapshot', () => {
     const shallow = new ShallowRenderer();
     shallow.render(<MyComponent />);
     const tree = shallow.getRenderOutput();
     expect(tree).toMatchSnapshot();
   });
-```
+``` 
 
 When dispalying that could require ternaries, don't use ternaries unless its really simple.
 For example: