test: isolate optional frontend dependency check

Author: FedorShind

tests/test_frontends.py

@@ -72,10 +72,20 @@ def test_explicit_optional_frontend_for_qiskit_raises_mismatch() -> None:
         detect_frontend(_qiskit_bell(), frontend="braket")
 
 
-def test_explicit_optional_frontend_missing_dependency_has_install_hint() -> None:
+def test_explicit_optional_frontend_missing_dependency_has_install_hint(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
     class UnknownCircuit:
         pass
 
+    def missing_braket(_frontend: Frontend) -> type:
+        raise frontends.FrontendDependencyError(
+            "frontend='braket' requires optional Braket support.\n"
+            'Install with: pip install "emrg[braket]"'
+        )
+
+    monkeypatch.setattr(frontends, "_load_frontend_type", missing_braket)
+
     with pytest.raises(
         ImportError,
         match=(