diff --git a/init.lua b/init.lua
index 148e481..6fa0ca4 100644
--- a/init.lua
+++ b/init.lua
@@ -105,6 +105,28 @@ end
         engine.test.equals(#empty, 0, "grep_engine_calls: empty -> 0")
     end
 
+    -- ===== generate_topology_block =====
+    do
+        -- Standard: lib with 1 dep + engine-calls
+        local manifest = {
+            id = "lib-core.foo",
+            deps = { {id="lib-core.bar"} }
+        }
+        local engine_calls = {"engine.input.is_action_down"}
+        local mermaid = api.generate_topology_block(manifest, engine_calls)
+        engine.test.assert(string.find(mermaid, "graph LR") or string.find(mermaid, "graph TD"),
+                          "generate_topology_block: starts with graph directive")
+        engine.test.assert(string.find(mermaid, "lib%-core%.foo", 1, false), "generate_topology_block: self-node present")
+        engine.test.assert(string.find(mermaid, "lib%-core%.bar", 1, false), "generate_topology_block: dep-node present")
+        engine.test.assert(string.find(mermaid, "engine%.%*", 1, false),     "generate_topology_block: engine-node present")
+
+        -- Asset-Lib: no deps, no engine-calls
+        local asset = { id = "lib-asset.sprites", deps = {} }
+        local asset_mermaid = api.generate_topology_block(asset, {})
+        engine.test.assert(string.find(asset_mermaid, "lib%-asset%.sprites", 1, false), "generate_topology_block: asset-lib has self-node")
+        engine.test.assert(not string.find(asset_mermaid, "engine%.%*", 1, false), "generate_topology_block: asset-lib has no engine-node")
+    end
+
     engine.exit(engine.test.failures())
 end