Implement test for graph ahead and behind

tests/graph/ahead_behind.c

+#include "clar_libgit2.h"
+
+static git_repository *_repo;
+static git_commit *commit;
+static size_t ahead;
+static size_t behind;
+
+void test_graph_ahead_behind__initialize(void)
+{
+	git_oid oid;
+	cl_git_pass(git_repository_open(&_repo, cl_fixture("testrepo.git")));
+
+	cl_git_pass(git_oid_fromstr(&oid, "be3563ae3f795b2b4353bcce3a527ad0a4f7f644"));
+	cl_git_pass(git_commit_lookup(&commit, _repo, &oid));
+}
+
+void test_graph_ahead_behind__cleanup(void)
+{
+	git_commit_free(commit);
+	commit = NULL;
+
+	git_repository_free(_repo);
+	_repo = NULL;
+}
+
+void test_graph_ahead_behind__returns_correct_result(void)
+{	
+	git_oid oid;
+	git_oid oid2;
+	git_commit *other;
+
+	cl_git_pass(git_oid_fromstr(&oid, "e90810b8df3e80c413d903f631643c716887138d"));
+	cl_git_pass(git_oid_fromstr(&oid2, "be3563ae3f795b2b4353bcce3a527ad0a4f7f644"));
+	
+	cl_git_pass(git_graph_ahead_behind(&ahead, &behind, _repo, &oid, &oid2));
+	cl_assert_equal_sz(2, ahead);
+	cl_assert_equal_sz(6, behind);
+
+	cl_git_pass(git_graph_ahead_behind(&ahead, &behind, _repo, git_commit_id(commit), git_commit_id(commit)));
+	cl_assert_equal_sz(ahead, behind);
+	cl_git_pass(git_commit_nth_gen_ancestor(&other, commit, 1));
+
+	cl_git_pass(git_graph_ahead_behind(&ahead, &behind, _repo, git_commit_id(commit), git_commit_id(other)));
+	cl_assert_equal_sz(ahead, behind + 2);
+	cl_git_pass(git_graph_ahead_behind(&ahead, &behind, _repo, git_commit_id(other), git_commit_id(commit)));
+	cl_assert_equal_sz(ahead + 2, behind);
+
+	git_commit_free(other);
+
+	cl_git_pass(git_commit_nth_gen_ancestor(&other, commit, 3));
+
+	cl_git_pass(git_graph_ahead_behind(&ahead, &behind, _repo, git_commit_id(commit), git_commit_id(other)));
+	cl_assert_equal_sz(ahead, behind + 4);
+	cl_git_pass(git_graph_ahead_behind(&ahead, &behind, _repo, git_commit_id(other), git_commit_id(commit)));
+	cl_assert_equal_sz(ahead + 4, behind);
+
+	git_commit_free(other);
+}