--- a
+++ b/tests/test.activations.py
@@ -0,0 +1,49 @@
+from osim.env import L2RunEnv
+import numpy as np
+import unittest
+
+class ActivationsTest(unittest.TestCase):
+    def test_activations(self):
+        env = L2RunEnv(visualize=False)
+        observation = env.reset()
+
+        newact = np.array([0.0] * 18)
+        env.osim_model.set_activations(newact)
+        
+        current = np.array(env.osim_model.get_activations())
+        dist = np.linalg.norm(newact - current)
+        self.assertTrue(dist < 0.05)
+        
+        newact = np.array([1.0] * 18)
+        env.osim_model.set_activations(newact)
+
+        current = np.array(env.osim_model.get_activations())
+        dist = np.linalg.norm(newact - current)
+        self.assertTrue(dist < 0.05)
+
+    def test_activations_changes(self):
+        env = L2RunEnv(visualize=False)
+
+        # Do not set new activations
+        newAct = [0.9] * 18
+        observation = env.reset()
+        env.osim_model.set_activations(newAct)
+        for i in range(5): 
+            withoutAct = env.osim_model.get_activations()
+            observation, reward, done, info = env.step([0.5]*18)
+
+        # Set new activations
+        newAct = [0.1] * 18
+        observation = env.reset()
+        env.osim_model.set_activations(newAct)
+        for i in range(5): 
+            withAct = env.osim_model.get_activations()
+            observation, reward, done, info = env.step([0.5]*18)
+
+        dist = np.linalg.norm(np.array(withAct) - np.array(withoutAct))
+
+        self.assertFalse(dist < 1e-2,"Activations after 5 steps haven't changed (despite different initial conditions)")
+
+        
+if __name__ == '__main__':
+    unittest.main()