diff --git a/tests/succession_diagram_test.py b/tests/succession_diagram_test.py
index ad8d0cd..d8762cf 100644
--- a/tests/succession_diagram_test.py
+++ b/tests/succession_diagram_test.py
@@ -171,13 +171,13 @@ def test_expansion_comparisons(network_file: str):
         # succession_diagram is too large for this test.
         return
 
+    assert sd_bfs.is_isomorphic(sd_dfs)
+
     # Normal minimal trap space expansion.
     sd_min = SuccessionDiagram(bn)
     assert sd_min.expand_minimal_spaces(size_limit=NODE_LIMIT)
 
-    assert sd_bfs.is_isomorphic(sd_dfs)
     assert sd_min.is_subgraph(sd_bfs)
-    assert sd_min.is_subgraph(sd_dfs)
 
     # Expand the first node fully, and then expand the rest
     # until minimal trap spaces are found.
@@ -188,7 +188,6 @@ def test_expansion_comparisons(network_file: str):
             assert sd_min_larger.expand_minimal_spaces(node_id=node_id)
 
     assert sd_min_larger.is_subgraph(sd_bfs)
-    assert sd_min_larger.is_subgraph(sd_dfs)
     assert len(sd_min_larger) >= len(sd_min)
 
     # Normal block expansion with size limit.
@@ -200,7 +199,6 @@ def test_expansion_comparisons(network_file: str):
     )
 
     assert sd_block.is_subgraph(sd_bfs)
-    assert sd_block.is_subgraph(sd_dfs)
 
     block_trap = [
         sd_block.node_data(i)["space"] for i in sd_block.minimal_trap_spaces()
@@ -211,6 +209,19 @@ def test_expansion_comparisons(network_file: str):
     for t in min_trap:
         assert t in block_trap
 
+    # Block expansion with symbolic fallback.
+    sd_config = SuccessionDiagram.default_config()
+    # Artificially enforce that NFVS method (almost) always fails.
+    sd_config["attractor_candidates_limit"] = 0
+    sd_block_fallback = SuccessionDiagram(bn)
+    assert sd_block_fallback.expand_block(
+        find_motif_avoidant_attractors=True,
+        size_limit=NODE_LIMIT,
+        optimize_source_nodes=False,
+    )
+
+    sd_block_fallback.is_subgraph(sd_bfs)
+
     sd_attr = SuccessionDiagram(bn)
     assert sd_attr.expand_attractor_seeds(size_limit=NODE_LIMIT)