Add test for arrays being completely equal (#117)

* Add test for arrays being completely equal

It's a nearly useless test, but it does get is-shallow-equal to 100% test coverage
See https://codecov.io/gh/WordPress/packages/src/master/packages/is-shallow-equal/index.js#L48 for the one piece of code not currently tested.

* fix spacing

* add test for object copies

packages/is-shallow-equal/test/index.js

@@ -61,6 +61,13 @@ describe( 'isShallowEqual', () => {
 		expect( isShallowEqual( obj, obj ) ).toBe( true );
 	} );
 
+	it( 'returns true on objects that are a copy of each other', () => {
+		const a = { foo: 1 };
+		const b = a;
+
+		expect( isShallowEqual( a, b ) ).toBe( true );
+	} );
+
 	it( 'returns true on object deep-but-referentially-equal values', () => {
 		const obj = {};
 		const a = { foo: obj };
@@ -104,6 +111,13 @@ describe( 'isShallowEqual', () => {
 
 		expect( isShallowEqual( a, b ) ).toBe( true );
 	} );
+
+	it( 'returns true on arrays that are a copy of each other', () => {
+		const a = [];
+		const b = a;
+
+		expect( isShallowEqual( a, b ) ).toBe( true );
+	} );
 } );
 
 describe( 'isShallowEqualArrays', () => {