diff --git a/mrmustard/lab_dev/transformations/cxgate.py b/mrmustard/lab_dev/transformations/cxgate.py
index 6cc3115f1..5126abc54 100644
--- a/mrmustard/lab_dev/transformations/cxgate.py
+++ b/mrmustard/lab_dev/transformations/cxgate.py
@@ -62,7 +62,7 @@ def __init__(
                 f"The number of modes for a CXgate must be 2 (your input has {len(modes)} many modes)."
             )
         super().__init__(name="CXgate")
-        self.parameter_set.add_parameter(make_parameter(s_trainable, s, "s", s_bounds))
+        self._add_parameter(make_parameter(s_trainable, s, "s", s_bounds))
         symplectic = math.astensor(
             [
                 [1, 0, 0, 0],
diff --git a/mrmustard/lab_dev/transformations/czgate.py b/mrmustard/lab_dev/transformations/czgate.py
index 3e8e39aff..4bf582a89 100644
--- a/mrmustard/lab_dev/transformations/czgate.py
+++ b/mrmustard/lab_dev/transformations/czgate.py
@@ -64,7 +64,7 @@ def __init__(
                 f"The number of modes for a CZgate must be 2 (your input has {len(modes)} many modes)."
             )
         super().__init__(name="CZgate")
-        self.parameter_set.add_parameter(make_parameter(s_trainable, s, "s", s_bounds))
+        self._add_parameter(make_parameter(s_trainable, s, "s", s_bounds))
         symplectic = math.astensor(
             [
                 [1, 0, 0, 0],
diff --git a/mrmustard/lab_dev/transformations/interferometer.py b/mrmustard/lab_dev/transformations/interferometer.py
index 81796c73a..ccccd0867 100644
--- a/mrmustard/lab_dev/transformations/interferometer.py
+++ b/mrmustard/lab_dev/transformations/interferometer.py
@@ -56,7 +56,7 @@ def __init__(
         if unitary is None:
             unitary = math.random_unitary(num_modes)
         super().__init__(name="Interferometer")
-        self.parameter_set.add_parameter(
+        self._add_parameter(
             make_parameter(unitary_trainable, unitary, "unitary", (None, None), update_unitary)
         )
         symplectic = math.block(
diff --git a/mrmustard/lab_dev/transformations/mzgate.py b/mrmustard/lab_dev/transformations/mzgate.py
index cc0bbf0ce..950ed2ac7 100644
--- a/mrmustard/lab_dev/transformations/mzgate.py
+++ b/mrmustard/lab_dev/transformations/mzgate.py
@@ -62,12 +62,8 @@ def __init__(
         internal: bool = False,
     ):
         super().__init__(name="MZgate")
-        self.parameter_set.add_parameter(
-            make_parameter(phi_a_trainable, phi_a, "phi_a", phi_a_bounds)
-        )
-        self.parameter_set.add_parameter(
-            make_parameter(phi_b_trainable, phi_b, "phi_b", phi_b_bounds)
-        )
+        self._add_parameter(make_parameter(phi_a_trainable, phi_a, "phi_a", phi_a_bounds))
+        self._add_parameter(make_parameter(phi_b_trainable, phi_b, "phi_b", phi_b_bounds))
 
         ca = math.cos(phi_a)
         sa = math.sin(phi_a)
diff --git a/mrmustard/lab_dev/transformations/pgate.py b/mrmustard/lab_dev/transformations/pgate.py
index 09fdf8184..fbeeeede0 100644
--- a/mrmustard/lab_dev/transformations/pgate.py
+++ b/mrmustard/lab_dev/transformations/pgate.py
@@ -59,7 +59,7 @@ def __init__(
         shearing_bounds: tuple[float | None, float | None] = (None, None),
     ):
         super().__init__(name="Pgate")
-        self.parameter_set.add_parameter(
+        self._add_parameter(
             make_parameter(shearing_trainable, shearing, "shearing", shearing_bounds)
         )
 
diff --git a/mrmustard/lab_dev/transformations/realinterferometer.py b/mrmustard/lab_dev/transformations/realinterferometer.py
index 668615da0..76f1575bd 100644
--- a/mrmustard/lab_dev/transformations/realinterferometer.py
+++ b/mrmustard/lab_dev/transformations/realinterferometer.py
@@ -55,7 +55,7 @@ def __init__(
             orthogonal = math.random_orthogonal(num_modes)
 
         super().__init__(name="RealInterferometer")
-        self.parameter_set.add_parameter(
+        self._add_parameter(
             make_parameter(
                 orthogonal_trainable, orthogonal, "orthogonal", (None, None), update_orthogonal
             )
diff --git a/tests/test_lab_dev/test_transformations/test_pgate.py b/tests/test_lab_dev/test_transformations/test_pgate.py
new file mode 100644
index 000000000..4e6730c31
--- /dev/null
+++ b/tests/test_lab_dev/test_transformations/test_pgate.py
@@ -0,0 +1,45 @@
+# Copyright 2024 Xanadu Quantum Technologies Inc.
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Tests for the ``Pgate`` class."""
+
+# pylint: disable=missing-function-docstring, expression-not-assigned
+
+import pytest
+
+from mrmustard import math
+from mrmustard.lab_dev.states import Vacuum
+from mrmustard.lab_dev.transformations import Pgate
+
+
+class TestPgate:
+    r"""
+    Tests for the ``Pgate`` class.
+    """
+
+    def test_init(self):
+        "Tests the Pgate initialization."
+        up = Pgate([0, 1], 0.3)
+        assert up.modes == [0, 1]
+        assert up.name == "Pgate"
+        assert up.shearing.value == 0.3
+
+    @pytest.mark.parametrize("s", [0.1, 0.5, 1])
+    def test_application(self, s):
+        "Tests if Pgate is being applied correctly."
+        up = Pgate([0], s)
+        rho = Vacuum([0]) >> up
+        cov, _, _ = rho.phase_space(s=0)
+        temp = math.astensor([[1, 0], [s, 1]], dtype="complex128")
+        assert math.allclose(cov[0], temp @ math.eye(2) @ temp.T / 2)