Add realpath variants of the commands that return paths.

Closes #1670.

test/src/test_command_path.h

@@ -0,0 +1,30 @@
+#include "test/helpers/test_fixture.h"
+
+#include <string>
+
+class TestCommandPath : public test_fixture {
+  CPPUNIT_TEST_SUITE(TestCommandPath);
+
+  CPPUNIT_TEST(test_resolves_symlink);
+  CPPUNIT_TEST(test_removes_relative_components);
+  CPPUNIT_TEST(test_expands_tilde);
+  CPPUNIT_TEST(test_missing_path_is_empty);
+  CPPUNIT_TEST(test_missing_path_throws);
+  CPPUNIT_TEST(test_commands);
+
+  CPPUNIT_TEST_SUITE_END();
+
+public:
+  void setUp();
+  void tearDown();
+
+  void test_resolves_symlink();
+  void test_removes_relative_components();
+  void test_expands_tilde();
+  void test_missing_path_is_empty();
+  void test_missing_path_throws();
+  void test_commands();
+
+private:
+  std::string m_temp_dir;
+};