added another snapshot test

frontend/src/__tests__/DropDown.snapshot.test.tsx

+import React from 'react'
+import DropDown from "../Components/DropDown"
+import renderer from 'react-test-renderer'
+
+it('renders correctly', () => {
+    const tree = renderer
+        .create(<DropDown/>)
+        .toJSON();
+    expect(tree).toMatchSnapshot()
+})

frontend/src/__tests__/__snapshots__/ArtPage.snapshot.test.tsx.snap

@@ -57,6 +57,7 @@ exports[`renders correctly 1`] = `
     className="navbutton left"
   >
     <img
+      alt="left"
       onClick={[Function]}
       src="left-arrow.png"
       style={
@@ -71,6 +72,7 @@ exports[`renders correctly 1`] = `
     className="navbutton right"
   >
     <img
+      alt="right"
       onClick={[Function]}
       src="right-arrow.png"
       style={

frontend/src/__tests__/__snapshots__/DropDown.snapshot.test.tsx.snap

+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`renders correctly 1`] = `
+<div
+  className="dropdown"
+>
+  <span
+    className="settings-icon"
+    onClick={[Function]}
+  />
+</div>
+`;