Create greatest common divisor exercise

greatest_common_divisor.lua

@@ -0,0 +1,23 @@
+-- Solution --------------------------------------------------------------------
+
+function greatest_common_divisor(x, y)
+   -- Your implementation here
+end
+
+-- Tests -----------------------------------------------------------------------
+
+local luaunit = require("luaunit.luaunit")
+
+function test_greatest_common_divisor_of_1386_and_3213_is_63()
+   luaunit.assertEquals(greatest_common_divisor(1386, 3213), 63)
+end
+
+function test_greatest_common_divisor_of_1470_and_3234_is_294()
+   luaunit.assertEquals(greatest_common_divisor(1470, 3234), 294)
+end
+
+function test_greatest_common_divisor_of_931_and_399_is_133()
+   luaunit.assertEquals(greatest_common_divisor(931, 399), 133)
+end
+
+os.exit(luaunit.LuaUnit.run())