Add unit test for AtomSpace crash.

The crash was reported in
#20

The fix is in
opencog/atomspace#3037

tests/persist/rocks/CMakeLists.txt

@@ -38,6 +38,7 @@ ADD_GUILE_TEST(FrameDelete frame-delete-test.scm)
 ADD_GUILE_TEST(FrameProgressive frame-progressive-test.scm)
 ADD_GUILE_TEST(FrameLinks frame-links-test.scm)
 ADD_GUILE_TEST(FrameValues frame-values-test.scm)
+ADD_GUILE_TEST(FramePrint frame-print-test.scm)
 ADD_GUILE_TEST(Promote promote-test.scm)
 #
 ADD_CXXTEST(LargeFlatUTest)

tests/persist/rocks/frame-print-test.scm

@@ -0,0 +1,52 @@
+;
+; frame-print-test.scm
+; Test for crash (null-pointer deref) for a simple usercase.
+;
+; The crash was in AtomSpace code.
+; See https://github.com/opencog/atomspace-rocks/issues/20
+; for details.
+; The fix is in https://github.com/opencog/atomspace/pull/3037
+;
+(use-modules (srfi srfi-1))
+(use-modules (opencog) (opencog test-runner))
+(use-modules (opencog persist) (opencog persist-rocks))
+
+(include "test-utils.scm")
+(whack "/tmp/cog-rocks-unit-test")
+
+(opencog-test-runner)
+
+; -------------------------------------------------------------------
+; Test that load of a series of nested links is done correctly.
+
+(define (test-print)
+
+	(define a (AtomSpace))
+	(define b (AtomSpace))
+	(define c (AtomSpace a b))
+
+	(cog-set-atomspace! a)
+	(Concept "I'm in A")
+	(cog-prt-atomspace)
+
+	(cog-set-atomspace! b)
+	(Concept "I'm in B")
+	(cog-prt-atomspace)
+
+	(cog-set-atomspace! c)
+	(define rsn (RocksStorageNode "rocks:///tmp/cog-rocks-unit-test"))
+	(cog-open rsn)
+	(store-atomspace)
+	(cog-prt-atomspace)
+
+	(cog-close rsn)
+)
+
+(define test-name "test print")
+(test-begin test-name)
+(test-print)
+(test-end test-name)
+
+; ===================================================================
+(whack "/tmp/cog-rocks-unit-test")
+(opencog-test-end)