[SimpleConf] Expand tests, add tiny quality tweaks

Tests/SimpleConf/CMakeLists.txt

@@ -16,6 +16,7 @@ target_sources(TestSimpleConf
     Comments.cpp
     Conversions.cpp
     EmptyConfigs.cpp
+    Files.cpp
     Optionality.cpp
     Parsing.cpp
     WhitespaceBehaviour.cpp

Tests/SimpleConf/Files.cpp

@@ -0,0 +1,23 @@
+#include <catch2/catch_test_macros.hpp>
+#include <Garbage/SimpleConf.hpp>
+
+TEST_CASE("Interactions with files")
+{
+    SECTION("Try loading a nonexistent file")
+    {
+        using ReadError = Garbage::SimpleConfImplementation::ReadError;
+
+        std::filesystem::path path("TestConfigs/ThisOneShouldntExist.conf");
+
+        REQUIRE_THROWS_AS(Garbage::SimpleConf(path), ReadError);
+    }
+
+    SECTION("Try loading a directory")
+    {
+        using ReadError = Garbage::SimpleConfImplementation::ReadError;
+
+        std::filesystem::path path("TestConfigs");
+
+        REQUIRE_THROWS_AS(Garbage::SimpleConf(path), ReadError);
+    }
+}