Extract GetLongestSuffix and add quick test

lc.vim

@@ -5,21 +5,32 @@ class Item
     const val: string
 endclass
 
-def GetMatch(base: string, line: string, add_base: bool): Item
-    var s = base
-    while stridx(line, s) == -1
+def GetLongestSuffix(hay: string, ndl: string): string
+    var s = ndl
+    var l = len(ndl)
+    while stridx(hay, s) == -1
         s = strpart(s, 1)
-        if strlen(s) == 0
-            return Item.new(0, "")
+        l = l - 1
+        if l == 0
+            return ""
         endif
     endwhile
+    return s
+enddef
+# echo GetLongestSuffix("hello world", "world")->assert_equal("world")
+# echo GetLongestSuffix("hello world", "foo world")->assert_equal("o world")
+# echo GetLongestSuffix("hello world foo bar blah", "foo world")->assert_equal("o world")
+# echo v:errors
+
+def GetMatch(base: string, line: string, add_base: bool): Item
+    const s = GetLongestSuffix(line, base)
     const idx = stridx(line, s)
     const slen = strlen(s)
+    const  m = strpart(line, idx + slen)
     if add_base
-        return Item.new(slen, base .. strpart(line, idx + slen))
-    else
-        return Item.new(slen, strpart(line, idx + slen))
+        return Item.new(slen, base .. m)
     endif
+    return Item.new(slen, m)
 enddef
 
 def GetMatches(base: string, add_base: bool): list<string>
@@ -30,9 +41,9 @@ def GetMatches(base: string, add_base: bool): list<string>
         ->sort()
         ->uniq()
         ->map( (_, v) => GetMatch(base, v, add_base) )
-        ->filter( (_, i) => i.len > 3 )
+        ->filter( (_, m) => m.len > 3 )
         ->sort( (x, y) => y.len - x.len )
-        ->map( (_, i) => i.val )
+        ->map( (_, m) => m.val )
 enddef
 
 def LineSuffixCompl(findstart: bool, base: string): any