diff --git a/doc/changelog.d/4185.maintenance.md b/doc/changelog.d/4185.maintenance.md
new file mode 100644
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+++ b/doc/changelog.d/4185.maintenance.md
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+Add InProcess testing module
diff --git a/tests/test_inprocess.py b/tests/test_inprocess.py
new file mode 100644
index 0000000000..35b5d69023
--- /dev/null
+++ b/tests/test_inprocess.py
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+# Copyright (C) 2016 - 2025 ANSYS, Inc. and/or its affiliates.
+# SPDX-License-Identifier: MIT
+#
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+import os
+import subprocess
+import sys
+from typing import TYPE_CHECKING
+
+import pytest
+
+if TYPE_CHECKING:
+    from ansys.mapdl.core import Mapdl
+
+from conftest import ON_LOCAL
+
+
+class MapdlInProcessRunner:
+    def __init__(self, wdir: str, version: float, exec_path: str | None = None) -> None:
+        self.wdir = str(wdir)
+        self.version = version
+        self.completed_process: subprocess.CompletedProcess[bytes] | None = None
+        self._exec_path: str | None = exec_path
+        self._output: str | None = None
+
+        # Detecting the venv
+        if sys.prefix == sys.base_prefix:
+            pytest.warns("Running from global python interpreter is not recommended.")
+        os.environ["MAPDL_PYTHON_ENV"] = sys.prefix
+
+    @property
+    def exec_path(self) -> str:
+        if self._exec_path is None:
+
+            self._exec_path = os.getenv("PYMAPDL_MAPDL_EXEC")
+            if self._exec_path is None:
+                from ansys.tools.path import get_mapdl_path
+
+                version: float | None = (
+                    float(os.getenv("PYMAPDL_MAPDL_VERSION", 0)) or None
+                )
+                self._exec_path = get_mapdl_path(version=version)
+
+        if self._exec_path is None:
+            raise ValueError(
+                "MAPDL executable path is not set. Set the PYMAPDL_MAPDL_EXEC "
+                "environment variable or use get_mapdl_path() to find it."
+            )
+
+        return self._exec_path
+
+    @property
+    def stdout(self) -> str | None:
+        """Return the standard output of the completed process. If the process fail, this returns None."""
+        if self.completed_process:
+            return self.completed_process.stdout.decode()
+
+    @property
+    def stderr(self) -> str | None:
+        """Return the standard error output of the completed process. If the process fail, this returns None."""
+        if self.completed_process:
+            return self.completed_process.stderr.decode()
+
+    @property
+    def status_code(self) -> float | None:
+        """Return the status code of the completed process. If the process fail, this returns None."""
+        if self.completed_process:
+            return float(self.completed_process.returncode)
+
+    @property
+    def exist_output(self) -> bool:
+        """Return True if the output file exists, False otherwise."""
+        return os.path.exists(os.path.join(self.wdir, "out.out"))
+
+    def output(self) -> str | None:
+        if not self._output and self.exist_output:
+            with open(os.path.join(self.wdir, "out.out"), "r") as f:
+                self._output = f.read()
+        return self._output
+
+    def run(self, cmds: str) -> str | None:
+        """Run commands in MAPDL on batch mode."""
+        with open(os.path.join(self.wdir, "input.mac"), "w") as f:
+            f.write(cmds)
+
+        exec_path = self.exec_path
+        # Security: Validate the executable path
+        if not os.path.isabs(exec_path) or not os.path.isfile(exec_path):
+            raise ValueError(
+                "MAPDL executable path must be an absolute path to an existing file."
+            )
+
+        try:
+            args = [
+                exec_path,
+                "-b",
+                "-i",
+                "input.mac",
+                "-o",
+                "out.out",
+                os.getenv("PYMAPDL_ADDITIONAL_SWITCHES", ""),
+            ]
+
+            self.completed_process = subprocess.run(
+                args=args,
+                cwd=self.wdir,
+                check=True,
+                capture_output=True,
+                # # it does not support shell=True, because it does not
+                # # generate the out.out file
+                # # TODO: Why shell should be false in order to generate the output file?
+                shell=False,  # nosec B603
+            )
+
+        except subprocess.CalledProcessError as e:
+            error_msg = (
+                f"MAPDL execution failed with return code {e.returncode}.\n"
+                f"Command: {' '.join(e.cmd)}\n"
+                f"Stdout:\n{e.stdout.decode() if e.stdout else ''}\n"
+                f"Stderr:\n{e.stderr.decode() if e.stderr else ''}\n"
+            )
+            pytest.fail(error_msg)
+
+        return self.output()
+
+
+@pytest.fixture()
+def mapdl_version(mapdl: "Mapdl"):
+    return mapdl.version
+
+
+@pytest.fixture()
+def mapdl_inprocess(mapdl_version: float, tmp_path: str) -> MapdlInProcessRunner:
+
+    # check if MAPDL has *PYTHON
+    if mapdl_version < 25.2:
+        pytest.skip("To test InProcess interface MAPDL 25.2 or higher is required")
+
+    if not ON_LOCAL:
+        pytest.skip("InProcess interface can only be tested on local machines")
+
+    if not (os.getenv("TEST_INPROCESS", "").lower() == "true"):
+        pytest.skip("Set TEST_INPROCESS environment variable to run them.")
+
+    mapdl_inprocess = MapdlInProcessRunner(tmp_path, version=mapdl_version)
+
+    return mapdl_inprocess
+
+
+def test_python_path(mapdl_inprocess: MapdlInProcessRunner):
+    """This test makes sure we are using the correct Python venv"""
+    cmds = """
+/com, Testing Python path
+*PYTHON
+import shutil
+print(shutil.which("python"))
+*ENDPY
+/com, test ends
+"""
+    output_content = mapdl_inprocess.run(cmds)
+    assert mapdl_inprocess.status_code == 0
+    assert output_content is not None
+    assert "Testing Python path" in output_content
+    assert sys.executable.replace("\\\\", "\\").lower() in output_content.lower()
+    assert "test ends" in output_content
+
+
+def test_start_python_from_pymapdl(
+    mapdl: "Mapdl", mapdl_inprocess: MapdlInProcessRunner
+):
+    # calling mapdl_inprocess just to make sure we do not
+    # run it in PyMAPDL versions below 25.2
+    output = mapdl.input_strings(
+        """
+*PYTHON
+print("Hello from MAPDL")
+*ENDPY
+"""
+    )
+
+    assert output is not None
+    assert "START PYTHON COMMAND BLOCK" in output
+    assert "Hello from MAPDL" in output
+    assert "END PYTHON COMMAND BLOCK" in output
+
+
+def test_start_python_from_mapdl(mapdl_inprocess: MapdlInProcessRunner):
+    """Test that MAPDL starts Python correctly."""
+    cmds = """
+/com, Starting Python commands
+*PYTHON
+print('Hello from MAPDL!')
+*ENDPY
+/com, test ends
+"""
+    output_content = mapdl_inprocess.run(cmds)
+    assert mapdl_inprocess.status_code == 0
+
+    assert output_content is not None
+    assert "Starting Python commands" in output_content
+    assert "Hello from MAPDL!" in output_content
+    assert "test ends" in output_content