refs: add tests for conditional updates

tests/refs/races.c

+#include "clar_libgit2.h"
+
+#include "repository.h"
+#include "git2/reflog.h"
+#include "reflog.h"
+#include "ref_helpers.h"
+
+static const char *commit_id = "099fabac3a9ea935598528c27f866e34089c2eff";
+static const char *refname = "refs/heads/master";
+static const char *other_commit_id = "a65fedf39aefe402d3bb6e24df4d4f5fe4547750";
+
+static git_repository *g_repo;
+
+void test_refs_races__initialize(void)
+{
+   g_repo = cl_git_sandbox_init("testrepo");
+}
+
+void test_refs_races__cleanup(void)
+{
+   cl_git_sandbox_cleanup();
+}
+
+void test_refs_races__create_matching(void)
+{
+	int error;
+	git_reference *ref, *ref2, *ref3;
+	git_oid id, other_id;
+
+	git_oid_fromstr(&id, commit_id);
+	git_oid_fromstr(&other_id, other_commit_id);
+
+	cl_git_fail_with(GIT_EMODIFIED, git_reference_create_matching(&ref, g_repo, refname, &other_id, 1, NULL, NULL, &other_id));
+
+	cl_git_pass(git_reference_lookup(&ref, g_repo, refname));
+	cl_git_pass(git_reference_create_matching(&ref2, g_repo, refname, &other_id, 1, NULL, NULL, &id));
+	cl_git_fail_with(GIT_EMODIFIED, git_reference_set_target(&ref3, ref, &other_id, NULL, NULL));
+
+	git_reference_free(ref);
+	git_reference_free(ref2);
+	git_reference_free(ref3);
+}