Added custom folder override mechanism for unit test files.

Custom/README

@@ -1,5 +1,5 @@
 If you need to modify already existing framework Perl module files or tt template files
-for customizations, you can do this in the $OTRS_HOME/Custom/ directory.
+or unit test files for customizations, you can do this in the $OTRS_HOME/Custom/ directory.
 
 Example:
 
@@ -10,5 +10,7 @@ Example:
 This method also works for tt files. Just place them in Kernel/Output/HTML/$ThemeName,
 and they will be used if the theme is selected.
 
+It also works for unit test files. Just place them in Custom/scripts/test.
+
 If you use Apache + mod_perl or PerlEx, any Perl module files placed in this directory
 will only be loaded by your web server after you restarted it.

Kernel/System/UnitTest.pm

@@ -141,6 +141,12 @@ sub Run {
             next FILE;
         }
 
+        # Check if a file with the same path and name exists in the Custom folder.
+        my $CustomFile = $File =~ s{ \A $Home }{$Home/Custom}xmsr;
+        if ( -e $CustomFile ) {
+            $File = $CustomFile;
+        }
+
         $Self->_HandleFile(
             PostTestScripts => $Param{PostTestScripts},
             File            => $File,