QA: Add WX_FILENAME split tests

Add some tests of the filename splitting of WX_FILENAME objects.

Interestingly, the result of GetFuillPath on an empty path is
likely wrong as it will imply an absolute path from /. But this is
probably not a used code path. Document the current behaviour as passing
the test.

This unit tests covers the code reported by Coverity 183884 and 183894
(improper use of negative). The find_last_of can return "npos" (-1), but
it's stored as a size_t. This is correct according the WX docs,
and the substr() method it is passed to can handle npos too.

qa/common/CMakeLists.txt

@@ -47,6 +47,7 @@ set( common_srcs
     test_title_block.cpp
     test_utf8.cpp
     test_wildcards_and_files_ext.cpp
+    test_wx_filename.cpp
 
     libeval/test_numeric_evaluator.cpp
 

qa/common/test_wx_filename.cpp

@@ -0,0 +1,129 @@
+/*
+ * This program source code file is part of KiCad, a free EDA CAD application.
+ *
+ * Copyright (C) 2019 KiCad Developers, see CHANGELOG.TXT for contributors.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you may find one here:
+ * http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
+ * or you may search the http://www.gnu.org website for the version 2 license,
+ * or you may write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
+ */
+
+/**
+ * @file
+ * Test suite for WX_FILNAME
+ */
+
+#include <unit_test_utils/unit_test_utils.h>
+
+// Code under test
+#include <common.h>
+
+/**
+ * Declare the test suite
+ */
+BOOST_AUTO_TEST_SUITE( WxFilename )
+
+
+struct WX_FILENAME_SPLIT_CASE
+{
+    // Ctor params
+    std::string m_path;
+    std::string m_name;
+
+    // Split results
+    std::string m_exp_name;
+    std::string m_exp_full_name;
+    std::string m_exp_path;
+    std::string m_exp_full_path;
+};
+
+
+// clang-format off
+static const std::vector<WX_FILENAME_SPLIT_CASE> split_cases = {
+    {
+        "",
+        "",
+        "",
+        "",
+        "",
+        "/", // This doesn't look right...
+    },
+    {
+        "",
+        "name.ext",
+        "name",
+        "name.ext",
+        "",
+        "/name.ext", // This doesn't look right...
+    },
+    {
+        "/tmp/example",
+        "",
+        "",
+        "",
+        "/tmp/example",
+        "/tmp/example/",
+    },
+    {
+        "/tmp/example",
+        "name.ext",
+        "name",
+        "name.ext",
+        "/tmp/example",
+        "/tmp/example/name.ext",
+    },
+    {
+        "/tmp/example",
+        "name", // no extension
+        "name",
+        "name",
+        "/tmp/example",
+        "/tmp/example/name",
+    },
+    {
+        "/tmp/example",
+        "name.ext1.ext2", // two extensions
+        "name.ext1", // remove the first one
+        "name.ext1.ext2",
+        "/tmp/example",
+        "/tmp/example/name.ext1.ext2",
+    },
+};
+// clang-format on
+
+/**
+ * Check the various split cases work correctly
+ */
+BOOST_AUTO_TEST_CASE( Split )
+{
+    for( const auto& c : split_cases )
+    {
+        std::stringstream ss;
+        ss << c.m_path << ", " << c.m_name;
+        BOOST_TEST_CONTEXT( ss.str() )
+        {
+            // Const: all methods called must be const
+            const WX_FILENAME wx_fn( c.m_path, c.m_name );
+
+            BOOST_CHECK_EQUAL( c.m_exp_name, wx_fn.GetName() );
+            BOOST_CHECK_EQUAL( c.m_exp_full_name, wx_fn.GetFullName() );
+            BOOST_CHECK_EQUAL( c.m_exp_path, wx_fn.GetPath() );
+            BOOST_CHECK_EQUAL( c.m_exp_full_path, wx_fn.GetFullPath() );
+        }
+    }
+}
+
+BOOST_AUTO_TEST_SUITE_END()