diff --git a/drivers/tests/test_driver_contract.py b/drivers/tests/test_driver_contract.py
index 5e42ff6..5c00fcb 100644
--- a/drivers/tests/test_driver_contract.py
+++ b/drivers/tests/test_driver_contract.py
@@ -72,12 +72,22 @@ def test_calls_set_make_in_init(self, driver_name):
             f"{driver_name}: should call host.set_make() in driver_init"
 
     def test_calls_emit_in_poll(self, driver_name):
-        """driver_poll should call host.emit()."""
+        """driver_poll should report something: a DER reading or metrics.
+
+        `host.emit` carries a DER reading and needs a DER type the host
+        understands. `heatpump` is in VALID_DERS, but no host has a heat-pump
+        reading type yet, so a heat-pump driver has nothing to emit and
+        reports temperatures and power through `host.emit_metric` instead.
+        Requiring `host.emit` of it would leave the author two options: emit
+        nothing, or claim to be a battery. Both are worse than a driver that
+        says what it measures.
+        """
         if driver_name == "hello":
             pytest.skip("hello driver is a demo-only driver")
         code = read_driver(driver_name)
-        assert 'host.emit(' in code, \
-            f"{driver_name}: should call host.emit() in driver_poll"
+        assert 'host.emit(' in code or 'host.emit_metric(' in code, \
+            f"{driver_name}: should call host.emit() or host.emit_metric() " \
+            f"in driver_poll"
 
     def test_no_forbidden_globals(self, driver_name):
         """Driver must not use forbidden sandbox-escaping functions."""
diff --git a/drivers/tests/test_mqtt_drivers.py b/drivers/tests/test_mqtt_drivers.py
index c9e78e0..167dfda 100644
--- a/drivers/tests/test_mqtt_drivers.py
+++ b/drivers/tests/test_mqtt_drivers.py
@@ -37,22 +37,36 @@ def test_subscribes_in_driver_init(self, driver_name):
             f"not elsewhere"
         )
 
-    def test_subscription_topics_are_strings(self, driver_name):
-        """All mqtt_subscribe calls should use string literal topics."""
+    def test_subscription_topics_are_static(self, driver_name):
+        """A subscription topic must be decidable without running the driver.
+
+        A literal is the common case. A configurable prefix is the other one:
+        heishamon and ctek_hybrid both build the topic from a file-local set
+        in driver_init, because the broker prefix is the operator's to choose.
+        That stays reviewable — every part is in the file.
+
+        What this rejects is a topic taken from runtime data: an index, a
+        field or a call, which is how a driver ends up subscribing to whatever
+        a message told it to.
+        """
         code = read_driver(driver_name)
         clean = strip_lua_comments(code)
 
-        # Find all subscribe calls and verify they use string literals
         sub_calls = re.findall(
             r'host\.mqtt_subscribe\s*\(\s*(.+?)\s*\)',
             clean,
         )
 
         for call_arg in sub_calls:
-            # Should be a string literal (starts with ")
-            assert call_arg.strip().startswith('"'), (
-                f"{driver_name}: mqtt_subscribe should use string literal "
-                f"topic, found: {call_arg}"
+            arg = call_arg.strip()
+            static = re.fullmatch(
+                r'(?:"[^"]*"|[A-Za-z_]\w*)'
+                r'(?:\s*\.\.\s*(?:"[^"]*"|[A-Za-z_]\w*))*',
+                arg,
+            )
+            assert static, (
+                f"{driver_name}: mqtt_subscribe topic must be a literal or a "
+                f"concatenation of literals and file-local names, found: {arg}"
             )