diff --git a/plugins/woocommerce-admin/client/components/chart/test/utils.js b/plugins/woocommerce-admin/client/components/chart/test/utils.js
index be29e6f94ad..1371a6660c3 100644
--- a/plugins/woocommerce-admin/client/components/chart/test/utils.js
+++ b/plugins/woocommerce-admin/client/components/chart/test/utils.js
@@ -11,6 +11,7 @@ import { utcParse as d3UTCParse } from 'd3-time-format';
  */
 import dummyOrders from './fixtures/dummy';
 import {
+	compareStrings,
 	getDateSpaces,
 	getOrderedKeys,
 	getLineData,
@@ -194,3 +195,11 @@ describe( 'getdateSpaces', () => {
 		expect( testDateSpaces[ testDateSpaces.length - 1 ].width ).toEqual( 10 );
 	} );
 } );
+
+describe( 'compareStrings', () => {
+	it( 'return an array of unique words from s2 that dont appear in base string', () => {
+		expect( compareStrings( 'Jul 2018', 'Aug 2018' ).join( ' ' ) ).toEqual( 'Aug' );
+		expect( compareStrings( 'Jul 2017', 'Aug 2018' ).join( ' ' ) ).toEqual( 'Aug 2018' );
+		expect( compareStrings( 'Jul 2017', 'Jul 2018' ).join( ' ' ) ).toEqual( '2018' );
+	} );
+} );
diff --git a/plugins/woocommerce-admin/client/components/chart/utils.js b/plugins/woocommerce-admin/client/components/chart/utils.js
index fbaee8da841..a181dee6463 100644
--- a/plugins/woocommerce-admin/client/components/chart/utils.js
+++ b/plugins/woocommerce-admin/client/components/chart/utils.js
@@ -357,6 +357,13 @@ export const getDateSpaces = ( data, uniqueDates, width, xLineScale ) =>
 		};
 	} );
 
+/**
+ * Compares 2 strings and returns a list of words that are unique from s2
+ * @param {string} s1 - base string to compare against
+ * @param {string} s2 - string to compare against the base string
+ * @param {string} splitChar - character to use to deliminate words
+ * @returns {array} of unique words that appear in s2 but not in s1, the base string
+ */
 export const compareStrings = ( s1, s2, splitChar = ' ' ) => {
 	const string1 = s1.split( splitChar );
 	const string2 = s2.split( splitChar );