Refactor add behavior for consistency between different usage

Now chain_Chainable a = new CustomChainable();
a.add(new CustomChainable()).add(new CustomChainable()).add(new CustomChainable())
will work the same as
chain_Chainable a = new CustomChainable();
a.add(new CustomChainable());
a.add(new CustomChainable());
a.add(new CustomChainable());

Author: scolladon

.gitignore

@@ -1 +1,2 @@
-.vscode
+.vscode
+.sfdx

force-app/main/default/classes/chain_Chainable.cls

@@ -28,12 +28,12 @@ public inherited sharing abstract class chain_Chainable {
   }*/
 
   public virtual chain_Chainable add(final chain_Chainable aChain) {
-    this.nextJob = aChain;
-    chain_Chainable tempChain = aChain;
-    while(tempChain != null && tempChain.nextJob != null) {
+    chain_Chainable tempChain = this.nextJob;
+    while(tempChain != null) {
       tempChain = tempChain.nextJob;
     }
-    return tempChain;
+    tempChain = aChain;
+    return this;
   }
 
   protected void chain() {

force-app/main/default/classes/chain_Chainable_TEST.cls

@@ -20,10 +20,10 @@ private class chain_Chainable_TEST {
     .Add(new chain_Schedule_TEST('test','0 0 * * * ?'))
     .Add(new chain_Future_TEST())
     .Add(new chain_Future_TEST())
-    .Add(new chain_ScheduleBatch_TEST('test',1,1))
-    .Add(new chain_Future_TEST())
-    .Add(new chain_Queue_TEST())
-    ;
+    .Add(new chain_ScheduleBatch_TEST('test',1,1));
+
+    aChainable.Add(new chain_Future_TEST());
+    aChainable.Add(new chain_Queue_TEST());
 
     test.startTest();
     aChainable.executeChain();