Two-node vfs2 unit test

src/vfs2.c

@@ -3,6 +3,7 @@
 #include "lib/byte.h"
 #include "lib/queue.h"
 #include "lib/sm.h"
+#include "tracing.h"
 #include "utils.h"
 
 #include <pthread.h>
@@ -1878,3 +1879,12 @@ int vfs2_pseudo_read_end(sqlite3_file *file, unsigned i)
 	e->shm_locks[i] -= 1;
 	return 0;
 }
+
+void vfs2_ut_sm_relate(sqlite3_file *orig, sqlite3_file *targ)
+{
+	struct file *forig = (struct file *)orig;
+	PRE(forig->flags & SQLITE_OPEN_MAIN_DB);
+	struct file *ftarg = (struct file *)targ;
+	PRE(ftarg->flags & SQLITE_OPEN_MAIN_DB);
+	sm_relate(&forig->entry->wtx_sm, &ftarg->entry->wtx_sm);
+}

src/vfs2.h

@@ -181,4 +181,13 @@ int vfs2_pseudo_read_end(sqlite3_file *file, unsigned i);
  */
 void vfs2_destroy(sqlite3_vfs *vfs);
 
+/**
+ * Declare a relationship between two databases opened by (possibly distinct)
+ * vfs2 instances.
+ *
+ * Intended for use by unit tests. The arguments are main file handles
+ * (SQLITE_FCNTL_FILE_POINTER).
+ */
+void vfs2_ut_sm_relate(sqlite3_file *orig, sqlite3_file *targ);
+
 #endif

test/unit/test_vfs2.c

@@ -388,9 +388,12 @@ TEST(vfs2, leader_and_follower, set_up, tear_down, 0, NULL)
 	OK(vfs2_poll(leader_fp, &frames, &leader_sl));
 	munit_assert_uint(leader_sl.len, ==, 2);
 
-	/* The follower receives the transaction. */
+	/* The follower opens its database. */
 	sqlite3 *follower_db = node_open_db(follower, "test.db");
 	sqlite3_file *follower_fp = main_file(follower_db);
+	vfs2_ut_sm_relate(leader_fp, follower_fp);
+
+	/* The follower receives the transaction. */
 	struct vfs2_wal_slice follower_sl;
 	OK(vfs2_add_uncommitted(follower_fp, PAGE_SIZE, frames, leader_sl.len,
 				&follower_sl));