Feature fix to lower case set list conversion issue (#3)

* Changed all refs to Set and update challenge wording

* null check

* fix the fix

---------

Co-authored-by: Saman Attar <[email protected]>

force-app/main/default/apexdeepdive/string/toLowerCase/ToLowerCase.md

@@ -31,7 +31,7 @@ System.debug(normalizedEmail); // Outputs: '[email protected]'
 ---
 ### Challenge: Using `toLowerCase()` for Email Deduplication
 
-You are tasked with cleaning up a set of email addresses in a Salesforce application. Due to various input methods and user errors, the set might contain emails with different case formats. Using `toLowerCase()`, you can standardize all email addresses to lowercase. 
+You are tasked with cleaning up a list of email addresses in a Salesforce application. Due to various input methods and user errors, the list might contain duplicate emails with different case formats. Using `toLowerCase()`, you can standardize all email addresses to lowercase to help identify and remove duplicates. 
 
 **Your task:**
-Write code that processes a set of email strings and converts each to lowercase.
+Write code that processes a list of email strings, converts each to lowercase, and then deduplicates the list. You will start with a predefined list of emails that includes potential duplicates with varying cases. Your method should return a set of strings. 

force-app/main/default/apexdeepdive/string/toLowerCase/ToLowerCaseSolution.cls

@@ -1,8 +1,9 @@
-public class ToLowerCaseSolution {
-    public Set<String> standardizeEmails(Set<String> emails) {
+public class StringUtils {
+    public Set<String> standardizeEmails(List<String> emails) {
+        Set<String> uniqueEmails = new Set<String>();
         for (String email : emails) {
-            email.toLowerCase();
+            uniqueEmails.add(email.toLowerCase());
         }
-        return emails;
+        return uniqueEmails;
     }
-}
+}

force-app/main/default/apexdeepdive/string/toLowerCase/ToLowerCaseTest.cls

@@ -28,10 +28,11 @@ public with sharing class ToLowerCaseTest {
         }
 
         public TestResult test1(String testNum) {
-            Set<String> emailsInput = new Set<String>{
+            List<String> emailsInput = new List<String>{
                 '[email protected]',
                 '[email protected]',
-                '[email protected]'
+                '[email protected]',
+                '[email protected]'
             };
             String testDesc = formatEmailSet(emailsInput);
 
@@ -45,7 +46,7 @@ public with sharing class ToLowerCaseTest {
             try {
                 Set<String> result = su.standardizeEmails(emailsInput);
 
-                if(!emailsSolution.containsAll(result)){
+                if(result == null || !emailsSolution.containsAll(result)){
                     msg =
                     'Expected ' +
                     emailsSolution +
@@ -60,7 +61,7 @@ public with sharing class ToLowerCaseTest {
         }
 
         public TestResult test2(String testNum) {
-            Set<String> emailsInput = new Set<String>{
+            List<String> emailsInput = new List<String>{
                 '[email protected]',
                 '[email protected]',
                 '[email protected]'
@@ -76,7 +77,7 @@ public with sharing class ToLowerCaseTest {
             try {
                 Set<String> result = su.standardizeEmails(emailsInput);
 
-                if(!emailsSolution.containsAll(result)){
+                if(result == null || !emailsSolution.containsAll(result)){
                     msg =
                     'Expected ' +
                     emailsSolution +