refs::namespace: add namespace tests

These simple tests only ensure that we enforce the existence of a
namespace; these mirror the rugged tests, they are not exhaustive.

tests/refs/namespaces.c

+#include "clar_libgit2.h"
+
+#include "repository.h"
+
+static git_repository *g_repo;
+
+void test_refs_namespaces__initialize(void)
+{
+	g_repo = cl_git_sandbox_init("testrepo");
+}
+
+void test_refs_namespaces__cleanup(void)
+{
+	cl_git_sandbox_cleanup();
+}
+
+void test_refs_namespaces__get_and_set(void)
+{
+	cl_assert_equal_s(NULL, git_repository_get_namespace(g_repo));
+
+	cl_git_pass(git_repository_set_namespace(g_repo, "namespace"));
+	cl_assert_equal_s("namespace", git_repository_get_namespace(g_repo));
+
+	cl_git_pass(git_repository_set_namespace(g_repo, NULL));
+	cl_assert_equal_s(NULL, git_repository_get_namespace(g_repo));
+}
+
+void test_refs_namespaces__namespace_doesnt_show_normal_refs(void)
+{
+	static git_strarray ref_list;
+
+	cl_git_pass(git_repository_set_namespace(g_repo, "namespace"));
+	cl_git_pass(git_reference_list(&ref_list, g_repo));
+	cl_assert_equal_i(0, ref_list.count);
+	git_strarray_free(&ref_list);
+}