[Minor] Microoptimize lua_util.str_endswith

Use find to check string suffix instead of sub (which involves string
interning of a returned string).  Benchmarks with LuaJIT 2.1.0 shows
that an option with find is significantly faster.

While here added unit test for this function.

1 files changed, 32 insertions, 1 deletions

diff --git a/test/lua/unit/lua_util.misc.lua b/test/lua/unit/lua_util.misc.lua
index b19b4d6f1..bab44a38b 100644
--- a/test/lua/unit/lua_util.misc.lua
+++ b/test/lua/unit/lua_util.misc.lua
@@ -27,4 +27,35 @@ context("Lua util - callback_from_string", function()
       assert_false(ret)
     end)
   end
-end)
\ No newline at end of file
+end)
+
+context("Lua util - str_endswith", function()
+  local ending = {
+    {'a', 'a'},
+    {'ab', 'b'},
+    {'ab', 'ab'},
+    {'abc', 'bc'},
+    {'any', ''},
+  }
+  local not_ending = {
+    {'a', 'b'},
+    {'', 'a'},
+    {'ab', 'a'},
+    {'ab', 'ba'},
+    {'ab', 'lab'},
+    {'abc', 'ab'},
+    {'abcd', 'bc'},
+    {'a', 'A'},
+    {'aB', 'b'},
+  }
+  for _, c in ipairs(ending) do
+    test(string.format('True case: str_endswith("%s", "%s")', c[1], c[2]), function()
+      assert_true(util.str_endswith(c[1], c[2]))
+    end)
+  end
+  for _, c in ipairs(not_ending) do
+    test(string.format('False case: str_endswith("%s", "%s")', c[1], c[2]), function()
+      assert_false(util.str_endswith(c[1], c[2]))
+    end)
+  end
+end)