diff --git a/tests/unit/vertexai/genai/replays/test_ae_sandboxes_private_create.py b/tests/unit/vertexai/genai/replays/test_ae_sandboxes_private_create.py
new file mode 100644
index 0000000000..7a6f822bee
--- /dev/null
+++ b/tests/unit/vertexai/genai/replays/test_ae_sandboxes_private_create.py
@@ -0,0 +1,38 @@
+# Copyright 2025 Google LLC
+#
+# 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.
+#
+# pylint: disable=protected-access,bad-continuation,missing-function-docstring
+
+from tests.unit.vertexai.genai.replays import pytest_helper
+from vertexai._genai import types
+
+
+def test_private_create(client):
+    spec = {
+        "code_execution_environment": {"machineConfig": "MACHINE_CONFIG_VCPU4_RAM4GIB"}
+    }
+    agent_engine_sandbox_operation = client.agent_engines.sandboxes._create(
+        name=(
+            "projects/964831358985/locations/us-central1/reasoningEngines/2886612747586371584"
+        ),
+        spec=spec,
+    )
+    assert isinstance(agent_engine_sandbox_operation, types.AgentEngineSandboxOperation)
+
+
+pytestmark = pytest_helper.setup(
+    file=__file__,
+    globals_for_file=globals(),
+    test_method="agent_engines.sandboxes._create",
+)
diff --git a/tests/unit/vertexai/genai/replays/test_ae_sandboxes_private_delete.py b/tests/unit/vertexai/genai/replays/test_ae_sandboxes_private_delete.py
new file mode 100644
index 0000000000..45c3eb4cb9
--- /dev/null
+++ b/tests/unit/vertexai/genai/replays/test_ae_sandboxes_private_delete.py
@@ -0,0 +1,36 @@
+# Copyright 2025 Google LLC
+#
+# 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.
+#
+# pylint: disable=protected-access,bad-continuation,missing-function-docstring
+
+from tests.unit.vertexai.genai.replays import pytest_helper
+from vertexai._genai import types
+
+
+def test_private_delete(client):
+    agent_engine_sandbox_delete_operation = client.agent_engines.sandboxes._delete(
+        name=(
+            "reasoningEngines/2886612747586371584/sandboxEnvironments/6068475153556176896"
+        ),
+    )
+    assert isinstance(
+        agent_engine_sandbox_delete_operation, types.DeleteAgentEngineSandboxOperation
+    )
+
+
+pytestmark = pytest_helper.setup(
+    file=__file__,
+    globals_for_file=globals(),
+    test_method="agent_engines.sandboxes._delete",
+)
diff --git a/tests/unit/vertexai/genai/replays/test_ae_sandboxes_private_execute_code.py b/tests/unit/vertexai/genai/replays/test_ae_sandboxes_private_execute_code.py
new file mode 100644
index 0000000000..ee07284663
--- /dev/null
+++ b/tests/unit/vertexai/genai/replays/test_ae_sandboxes_private_execute_code.py
@@ -0,0 +1,62 @@
+# Copyright 2025 Google LLC
+#
+# 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.
+#
+# pylint: disable=protected-access,bad-continuation,missing-function-docstring
+
+import json
+
+from tests.unit.vertexai.genai.replays import pytest_helper
+from vertexai._genai import types
+
+
+def test_private_execute_code(client):
+
+    code = """
+with open("test.txt", "r") as input:
+    with open("output.txt", "w") as output_txt:
+        for line in input:
+            output_txt.write(line)
+"""
+    # Transform the input data into chunks as expected by _execute_code
+    input_chunks = [
+        types.Chunk(
+            mime_type="application/json",
+            data=json.dumps({"code": code}).encode("utf-8"),
+        ),
+        types.Chunk(
+            mime_type="text/plain",
+            data=b"Hello, world!",
+            metadata={"attributes": {"file_name": b"test.txt"}},
+        ),
+    ]
+
+    execute_code_response = client.agent_engines.sandboxes._execute_code(
+        name=(
+            "reasoningEngines/2886612747586371584/sandboxEnvironments/6068475153556176896"
+        ),
+        inputs=input_chunks,
+    )
+    assert isinstance(
+        execute_code_response,
+        types.ExecuteSandboxEnvironmentResponse,
+    )
+    assert isinstance(execute_code_response.outputs, list)
+    assert isinstance(execute_code_response.outputs[0], types.Chunk)
+
+
+pytestmark = pytest_helper.setup(
+    file=__file__,
+    globals_for_file=globals(),
+    test_method="agent_engines.sandboxes._execute_code",
+)
diff --git a/tests/unit/vertexai/genai/replays/test_ae_sandboxes_private_get.py b/tests/unit/vertexai/genai/replays/test_ae_sandboxes_private_get.py
new file mode 100644
index 0000000000..35a3c41fb1
--- /dev/null
+++ b/tests/unit/vertexai/genai/replays/test_ae_sandboxes_private_get.py
@@ -0,0 +1,34 @@
+# Copyright 2025 Google LLC
+#
+# 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.
+#
+# pylint: disable=protected-access,bad-continuation,missing-function-docstring
+
+from tests.unit.vertexai.genai.replays import pytest_helper
+from vertexai._genai import types
+
+
+def test_private_get(client):
+
+    sandbox_name = "projects/964831358985/locations/us-central1/reasoningEngines/2886612747586371584/sandboxEnvironments/3186171392039059456"
+
+    agent_engine_sandbox = client.agent_engines.sandboxes._get(name=sandbox_name)
+    assert isinstance(agent_engine_sandbox, types.SandboxEnvironment)
+    assert agent_engine_sandbox.name == sandbox_name
+
+
+pytestmark = pytest_helper.setup(
+    file=__file__,
+    globals_for_file=globals(),
+    test_method="agent_engines.sandboxes._get",
+)
diff --git a/tests/unit/vertexai/genai/replays/test_ae_sandboxes_private_get_sandbox_operation.py b/tests/unit/vertexai/genai/replays/test_ae_sandboxes_private_get_sandbox_operation.py
new file mode 100644
index 0000000000..bdf1202372
--- /dev/null
+++ b/tests/unit/vertexai/genai/replays/test_ae_sandboxes_private_get_sandbox_operation.py
@@ -0,0 +1,38 @@
+# Copyright 2025 Google LLC
+#
+# 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.
+#
+# pylint: disable=protected-access,bad-continuation,missing-function-docstring
+
+from tests.unit.vertexai.genai.replays import pytest_helper
+from vertexai._genai import types
+
+
+def test_private_get_operation(client):
+
+    operation_name = (
+        "projects/964831358985/locations/us-central1/operations/4799455193970245632"
+    )
+
+    agent_engine_sandbox = client.agent_engines.sandboxes._get_sandbox_operation(
+        operation_name=operation_name
+    )
+    assert isinstance(agent_engine_sandbox, types.AgentEngineSandboxOperation)
+    assert agent_engine_sandbox.name == operation_name
+
+
+pytestmark = pytest_helper.setup(
+    file=__file__,
+    globals_for_file=globals(),
+    test_method="agent_engines.sandboxes._get_sandbox_operation",
+)
diff --git a/tests/unit/vertexai/genai/replays/test_ae_sandboxes_private_list.py b/tests/unit/vertexai/genai/replays/test_ae_sandboxes_private_list.py
new file mode 100644
index 0000000000..0457b49067
--- /dev/null
+++ b/tests/unit/vertexai/genai/replays/test_ae_sandboxes_private_list.py
@@ -0,0 +1,38 @@
+# Copyright 2025 Google LLC
+#
+# 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.
+#
+# pylint: disable=protected-access,bad-continuation,missing-function-docstring
+
+from tests.unit.vertexai.genai.replays import pytest_helper
+from vertexai._genai import types
+
+
+def test_private_list(client):
+    agent_engine_sandbox_list_operation = client.agent_engines.sandboxes._list(
+        name=("reasoningEngines/2886612747586371584"),
+    )
+    assert isinstance(
+        agent_engine_sandbox_list_operation.sandbox_environments[0],
+        types.SandboxEnvironment,
+    )
+    assert isinstance(
+        agent_engine_sandbox_list_operation, types.ListAgentEngineSandboxesResponse
+    )
+
+
+pytestmark = pytest_helper.setup(
+    file=__file__,
+    globals_for_file=globals(),
+    test_method="agent_engines.sandboxes._list",
+)