Use Catch for our test suite

`make check` is also added to compile and run the tests
Catch is fetched with cmake automatically into the build directory when needed

tests/utils.cpp

@@ -0,0 +1,72 @@
+#include "catch.hpp"
+
+#include <utils/tolower.hpp>
+#include <utils/revstr.hpp>
+#include <utils/string.hpp>
+#include <utils/split.hpp>
+#include <utils/xdg.hpp>
+
+TEST_CASE("String split")
+{
+  std::vector<std::string> splitted = utils::split("a::a", ':', false);
+  CHECK(splitted.size() == 2);
+  splitted = utils::split("a::a", ':', true);
+  CHECK(splitted.size() == 3);
+  CHECK(splitted[0] == "a");
+  CHECK(splitted[1] == "");
+  CHECK(splitted[2] == "a");
+  splitted = utils::split("\na", '\n', true);
+  CHECK(splitted.size() == 2);
+  CHECK(splitted[0] == "");
+  CHECK(splitted[1] == "a");
+}
+
+TEST_CASE("tolower")
+{
+  const std::string lowercase = utils::tolower("CoUcOu LeS CoPaiNs ♥");
+  CHECK(lowercase == "coucou les copains ♥");
+
+  const std::string ltr = "coucou";
+  CHECK(utils::revstr(ltr) == "uocuoc");
+}
+
+TEST_CASE("to_bool")
+{
+  CHECK(to_bool("true"));
+  CHECK(!to_bool("trou"));
+  CHECK(to_bool("1"));
+  CHECK(!to_bool("0"));
+  CHECK(!to_bool("-1"));
+  CHECK(!to_bool("false"));
+}
+
+TEST_CASE("xdg_*_path")
+{
+  ::unsetenv("XDG_CONFIG_HOME");
+  ::unsetenv("HOME");
+  std::string res;
+
+  SECTION("Without XDG_CONFIG_HOME nor HOME")
+    {
+      res = xdg_config_path("coucou.txt");
+      CHECK(res == "coucou.txt");
+    }
+  SECTION("With only HOME")
+    {
+      ::setenv("HOME", "/home/user", 1);
+      res = xdg_config_path("coucou.txt");
+      CHECK(res == "/home/user/.config/biboumi/coucou.txt");
+    }
+  SECTION("With only XDG_CONFIG_HOME")
+    {
+      ::setenv("XDG_CONFIG_HOME", "/some_weird_dir", 1);
+      res = xdg_config_path("coucou.txt");
+      CHECK(res == "/some_weird_dir/biboumi/coucou.txt");
+    }
+  SECTION("With XDG_DATA_HOME")
+    {
+      ::setenv("XDG_DATA_HOME", "/datadir", 1);
+      res = xdg_data_path("bonjour.txt");
+      CHECK(res == "/datadir/biboumi/bonjour.txt");
+    }
+}