Fix `formatPageIssuesSeverity`

The page-issues reducer function that retrieves the severityLevels
for issues was incorrectly comparing two values in the multiple-issues
scenario.

Instead of comparing the severity of the current issue with the previous
value in the accumulator, it was comparing the current issue with the
previous issue in the original array, thus ignoring the
previous `maxSeverity` value in the accumulator.

Tests added and function refactored with more explicit variable names.

Bug: T203725
Change-Id: Ia4c15cbf0c2457d68a7381e8ed04c1a6b3ae65d1

resources/skins.minerva.scripts/pageIssues.js

@@ -41,23 +41,27 @@
 	 * In the case that a page-issue is part of a "multiple issues" template,
 	 * returns the maximum severity for that group of issues.
 	 *
-	 * @param {array} acc - the return array containing severities
-	 * @param {IssueSummary} summary current IssueSummary object
+	 * @param {array} formattedArr - the return array containing severities
+	 * @param {IssueSummary} currentItem current IssueSummary object
 	 * @param {number} currentIndex current index of pageIssues
 	 * @param {array} pageIssues array of pageIssues
 	 *
 	 * @return {array} acc
 	 */
-	function formatPageIssuesSeverity( acc, summary, currentIndex, pageIssues ) {
-		var lastItem = pageIssues[ currentIndex - 1 ];
-		if ( lastItem && lastItem.isMultiple && summary.isMultiple ) {
-			acc[ acc.length - 1 ] = pageIssuesParser.maxSeverity(
-				[ lastItem.severity, summary.severity ]
+	function formatPageIssuesSeverity( formattedArr, currentItem, currentIndex, pageIssues ) {
+		var lastItem = pageIssues[ currentIndex - 1 ],
+			lastFormattedIndex = formattedArr.length - 1,
+			lastFormattedValue = formattedArr[ lastFormattedIndex ];
+		// If the last and current item `isMultiple`, fold the maxSeverity
+		// of the two items into a single value.
+		if ( lastItem && lastItem.isMultiple && currentItem.isMultiple ) {
+			formattedArr[ lastFormattedIndex ] = pageIssuesParser.maxSeverity(
+				[ lastFormattedValue, currentItem.severity ]
 			);
 		} else {
-			acc.push( summary.severity );
+			formattedArr.push( currentItem.severity );
 		}
-		return acc;
+		return formattedArr;
 	}
 
 	/**
@@ -336,6 +340,7 @@
 		// the subscription call in cleanuptemplates.
 		log: pageIssuesLogger.log,
 		test: {
+			formatPageIssuesSeverity: formatPageIssuesSeverity,
 			extractMessage: extractMessage,
 			getAllIssuesSections: getAllIssuesSections,
 			createBanner: createBanner

tests/qunit/skins.minerva.scripts/test_pageIssues.js

@@ -4,11 +4,24 @@
 		pageIssuesParser = M.require( 'skins.minerva.scripts/pageIssuesParser' ),
 		extractMessage = pageIssues.test.extractMessage,
 		createBanner = pageIssues.test.createBanner,
+		formatPageIssuesSeverity = pageIssues.test.formatPageIssuesSeverity,
 		MEDIUM_ISSUE = {
 			severity: 'MEDIUM',
 			icon: 'i',
 			text: 't'
 		},
+		MEDIUM_MULTIPLE_ISSUE = {
+			severity: 'MEDIUM',
+			isMultiple: true,
+			icon: 'i',
+			text: 't'
+		},
+		LOW_MULTIPLE_ISSUE = {
+			severity: 'LOW',
+			isMultiple: true,
+			icon: 'i',
+			text: 't'
+		},
 		LOW_ISSUE = {
 			severity: 'LOW',
 			icon: 'i',
@@ -64,6 +77,35 @@
 		} );
 	} );
 
+	QUnit.test( 'formatPageIssuesSeverity', function ( assert ) {
+		var multipleIssues = [
+				MEDIUM_MULTIPLE_ISSUE,
+				LOW_MULTIPLE_ISSUE,
+				LOW_MULTIPLE_ISSUE
+			],
+			multipleSingleIssues = [
+				LOW_ISSUE,
+				HIGH_ISSUE,
+				MEDIUM_ISSUE
+			],
+			mixedMultipleSingle = [
+				HIGH_ISSUE,
+				LOW_MULTIPLE_ISSUE,
+				MEDIUM_MULTIPLE_ISSUE,
+				LOW_ISSUE,
+				MEDIUM_ISSUE,
+				HIGH_ISSUE
+			],
+			testMultiple = multipleIssues.reduce( formatPageIssuesSeverity, [] ),
+			testSingle = multipleSingleIssues.reduce( formatPageIssuesSeverity, [] ),
+			testMixed = mixedMultipleSingle.reduce( formatPageIssuesSeverity, [] );
+
+		assert.deepEqual( testMultiple, [ 'MEDIUM' ], 'Multiple issues return one maxSeverity value' );
+		assert.deepEqual( testSingle, [ 'LOW', 'HIGH', 'MEDIUM' ], 'Single issues return each corresponding severity' );
+		assert.deepEqual( testMixed, [ 'HIGH', 'MEDIUM', 'LOW', 'MEDIUM', 'HIGH' ], 'Mixed single/multiple return one value for multiples' );
+
+	} );
+
 	QUnit.test( 'extractMessage', function ( assert ) {
 		this.sandbox.stub( pageIssuesParser, 'parse' ).returns(
 			{