added file_helper tests

tests/file_helper.cpp

+/*
+* This content is released under the MIT License as specified in https://raw.githubusercontent.com/gabime/spdlog/master/LICENSE
+*/
+#include "includes.h"
+
+using namespace spdlog::details;
+
+static const std::string filename = "logs/file_helper_test.txt";
+
+size_t filesize2(const std::string& filename)
+{
+    std::ifstream ifs(filename, std::ifstream::ate | std::ifstream::binary);
+    if (!ifs)
+        throw std::runtime_error("Failed open file ");
+
+    return (size_t)ifs.tellg();
+}
+
+static void write_with_helper(file_helper &helper, size_t howmany)
+{
+    log_msg msg;
+    msg.formatted << std::string(howmany, '1');
+    helper.write(msg);
+}
+
+
+TEST_CASE("file_helper_filename", "[file_helper::filename()]]")
+{
+    prepare_logdir();
+
+    file_helper helper(false);
+    helper.open(filename);
+    REQUIRE(helper.filename() == filename);
+}
+
+
+
+TEST_CASE("file_helper_size", "[file_helper::size()]]")
+{
+    prepare_logdir();
+    auto expected_size = 123;
+    {
+        file_helper helper(true);
+        helper.open(filename);
+        write_with_helper(helper, expected_size);
+        REQUIRE(helper.size() == expected_size);
+    }
+    REQUIRE(filesize2(filename) == expected_size);
+}
+
+
+TEST_CASE("file_helper_exists", "[file_helper::file_exists()]]")
+{
+    prepare_logdir();
+    REQUIRE(!file_helper::file_exists(filename));
+    file_helper helper(false);
+    helper.open(filename);
+    REQUIRE(file_helper::file_exists(filename));
+}
+
+TEST_CASE("file_helper_reopen", "[file_helper::reopen()]]")
+{
+    prepare_logdir();
+    file_helper helper(true);
+    helper.open(filename);
+    write_with_helper(helper, 12);
+    REQUIRE(helper.size() == 12);
+    helper.reopen(true);
+    REQUIRE(helper.size() == 0);
+}
+
+TEST_CASE("file_helper_reopen2", "[file_helper::reopen(false)]]")
+{
+    prepare_logdir();
+    auto expected_size = 14;
+    file_helper helper(true);
+    helper.open(filename);
+    write_with_helper(helper, expected_size);
+    REQUIRE(helper.size() == expected_size);
+    helper.reopen(false);
+    REQUIRE(helper.size() == expected_size);
+}
+
+
+
+