Lua: refactored and extracted test approach

common/space_lua/stdlib/os_test.lua

@@ -0,0 +1,9 @@
+local function assert_equal(a, b)
+    if a ~= b then
+        error("Assertion failed: " .. a .. " is not equal to " .. b)
+    end
+end
+
+-- Basic OS functions
+assert(os.time() > 0)
+assert(os.date("%Y-%m-%d", os.time({ year = 2020, month = 1, day = 1 })) == "2020-01-01")