diff --git a/unittest/force-styles/tests/bond-nonlinear.yaml b/unittest/force-styles/tests/bond-nonlinear.yaml
index ae52190dd9..995d39425f 100644
--- a/unittest/force-styles/tests/bond-nonlinear.yaml
+++ b/unittest/force-styles/tests/bond-nonlinear.yaml
@@ -17,7 +17,10 @@ bond_coeff: ! |
   4 650.0 1.2 1.4
   5 450.0 1.0 1.1
 equilibrium: 5 1.5 1.1 1.3 1.2 1
-extract: ! ""
+extract: ! |
+  lamda 1
+  epsilon 1
+  r0 1
 natoms: 29
 init_energy: 1.9451728032820943
 init_stress: ! |-