Refactor logging code and update test cases

Author: mutouyun

include/libimp/log.h

@@ -105,21 +105,31 @@ inline auto &make_std_out() noexcept {
   return std_out;
 }
 
+/**
+ * \brief Log information base class.
+ */
+class logger_base {
+protected:
+  char const *func_;
+  level level_limit_;
+
+  logger_base(char const *func, level level_limit) noexcept
+    : func_       (func)
+    , level_limit_(level_limit) {}
+};
+
 /**
  * \brief Log information grips.
  */
 template <typename Outputer>
-class logger {
+class logger : public logger_base {
   Outputer out_;
-  char const *func_;
-  level level_limit_;
 
 public:
   template <typename O>
-  logger(char const *func, O &&out, level level_limit) noexcept 
-    : out_        (std::forward<O>(out))
-    , func_       (func)
-    , level_limit_(level_limit) {}
+  logger(char const *func, O &&out, level level_limit) noexcept
+    : logger_base(func, level_limit)
+    , out_       (std::forward<O>(out)) {}
 
   template <typename... A>
   logger const &operator()(log::level l, A &&...args) const noexcept {

test/imp/test_imp_log.cpp

@@ -17,7 +17,7 @@ TEST(log, logger) {
   }
   {
     LIBIMP_LOG_();
-    log.info(), "hello ", 3;
+    log.info("hello ", 3);
   }
   SUCCEED();
 }
@@ -36,11 +36,11 @@ TEST(log, custom) {
 
   LIBIMP_LOG_(ll);
 
-  log.info ("hello");
-  log.error("failed:");
-  log.info ("log-pt");
+  log.info ("hello", " world");
+  log.error("failed", ":");
+  log.info ("log", '-', "pt");
   log.error("whatever");
 
-  EXPECT_EQ(ll_data.i, "hello log-pt ");
+  EXPECT_EQ(ll_data.i, "hello world log-pt ");
   EXPECT_EQ(ll_data.e, "failed: whatever ");
 }