Prevent Brownian dynamics coupling of virtual sites (espressomd#4295)

src/python/espressomd/thermostat.pyx

@@ -407,16 +407,15 @@ cdef class Thermostat:
             The same applies to ``gamma_rotation``, which requires the feature
             ``ROTATION`` to work properly. But also accepts three floats
             if ``PARTICLE_ANISOTROPY`` is also compiled in.
-        act_on_virtual : :obj:`bool`, optional
-            If ``True`` the thermostat will act on virtual sites, default is
-            ``False``.
         seed : :obj:`int`
             Initial counter value (or seed) of the philox RNG.
             Required on first activation of the Brownian thermostat.
             Must be positive.
 
         """
 
+        assert act_on_virtual is False, "Brownian dynamics virtual sites coupling was disabled in ESPResSo 4.2.2"
+
         scalar_gamma_def = True
         scalar_gamma_rot_def = True
         IF PARTICLE_ANISOTROPY:

testsuite/python/brownian_dynamics.py

@@ -144,14 +144,6 @@ def test_07__virtual(self):
         np.testing.assert_almost_equal(np.copy(virtual.v), [1, 0, 0])
         np.testing.assert_almost_equal(np.copy(physical.v), [0, 0, 0])
 
-        virtual.pos = physical.pos = [0, 0, 0]
-        system.thermostat.set_brownian(
-            kT=0, gamma=1, gamma_rotation=1., act_on_virtual=True, seed=41)
-        system.integrator.run(1)
-
-        np.testing.assert_almost_equal(np.copy(virtual.v), [0, 0, 0])
-        np.testing.assert_almost_equal(np.copy(physical.v), [0, 0, 0])
-
     @utx.skipIfMissingFeatures(["ROTATION", "EXTERNAL_FORCES"])
     def test_fix_rotation(self):
         system = self.system
@@ -168,8 +160,7 @@ def test_fix_rotation(self):
         system.integrator.set_brownian_dynamics()
         system.integrator.run(3)
         np.testing.assert_allclose(
-            part.omega_lab, [
-                0, 0, 1.3 / 1.5], atol=1e-14)
+            part.omega_lab, [0, 0, 1.3 / 1.5], atol=1e-14)
 
         # noise only
         part.ext_torque = 3 * [0.]