aga: Testcase for attempt to run concurrent algorithms

The aga algorithms can't be run concurrently, because they store state
information in the aga_node structures.  However, they are supposed to
detect an attempt to re-enter and safely report an error.  This adds a
testcase for this.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

ccan/aga/test/api-concurrent.c

+#include "config.h"
+
+#include <stddef.h>
+#include <assert.h>
+
+#include <ccan/aga/aga.h>
+
+#include <ccan/tap/tap.h>
+
+#include "simple-graph.h"
+
+
+#define NUM_ALGOS	2
+
+#define check_one_inner(algo) \
+	ok1(aga_##algo##_start(&tg.sg.g) == -1);
+
+#define check_all_inner()			\
+	do {					\
+		check_one_inner(dfs);		\
+		check_one_inner(bfs);		\
+	} while (0)
+
+#define check_one_outer(algo)					\
+	do {							\
+		ok1(aga_##algo##_start(&tg.sg.g) == 0);		\
+		check_all_inner();				\
+		aga_finish(&tg.sg.g);				\
+	} while (0)
+
+#define check_all_outer()			\
+	do {					\
+		check_one_outer(dfs);		\
+		check_one_outer(bfs);		\
+	} while (0)
+
+int main(void)
+{
+	struct trivial_graph tg;
+
+	if (NUM_ALGOS)
+		plan_tests(NUM_ALGOS + NUM_ALGOS * NUM_ALGOS);
+	else
+		plan_skip_all("Nothing to test");
+
+	trivial_graph_init(&tg);
+
+	check_all_outer();
+
+	/* This exits depending on whether all tests passed */
+	return exit_status();
+}