diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 84f6c7bfacae235c908c603e1ea02f64ff5a6912..e5582169621ce6309ed68e9e1f18cf6ee64788c3 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -45,3 +45,14 @@ run-executable:
   needs:
     - job: build-executable
       artifacts: true
+
+pytest:
+  extends: .python3
+  stage: test
+  before_script:
+    - poetry install
+  script:
+    - poetry run pytest --junit-xml test.xml
+  artifacts:
+    reports:
+      junit: test.xml
diff --git a/mnpw/__init__.py b/mnpw/__init__.py
index 5c38cf9243fdbf495dc2433432047f176b21e5da..a20a024dbd7e9e59eaf21a5301d70940fce6e09f 100644
--- a/mnpw/__init__.py
+++ b/mnpw/__init__.py
@@ -52,7 +52,7 @@ def main():
     check = nagios.Check(args.command, args.arguments)
     try:
         check.run(args.timeout, args.dry_run)
-    except Exception as ex:
+    except Exception as ex:  # pylint: disable=broad-except
         parser.error(str(ex))
 
 
diff --git a/mnpw/nagios.py b/mnpw/nagios.py
index d396c8e96c18fe90ca60fbab0524ebc92fd7176e..b263fdda266937054a9a25b52e664e3f2b5cf581 100644
--- a/mnpw/nagios.py
+++ b/mnpw/nagios.py
@@ -1,7 +1,10 @@
-"""Nagios check implementation."""
+"""Nagios check implementation.
+
+Based on the specification from
+https://assets.nagios.com/downloads/nagioscore/docs/nagioscore/3/en/pluginapi.html"""
 
 import enum
-import subprocess
+import subprocess  # nosemgrep: rules.bandit.B404
 
 DEFAULT_TIMEOUT = 10  # In seconds.
 
@@ -21,11 +24,11 @@ class Check:
     Command = None
     Arguments = []
     ExitCode = None
-    Result = None
     Output = None
     PerfData = None
+    LongOutput = None
     AdditionalOutput = None
-    StandardError = None
+    stderr = None
 
     def __init__(self, command, args):
         if not command:
@@ -34,9 +37,16 @@ class Check:
         if args:
             self.Arguments = args
 
-    def run(self, timeout=DEFAULT_TIMEOUT, dryrun=False):
+    def _parse_output(self):
+        """Parses the plugin output to get the output, perf data and long
+        output. Can be run after the plugin has run and finished
+        successfully."""
+        if self.ExitCode is None:
+            raise RuntimeError("Check hasn't run yet.")
+
+    def run(self, timeout=DEFAULT_TIMEOUT):
         """Run the check (if it's hasn't run yet)."""
-        if self.Result is not None:
+        if self.ExitCode is not None:
             raise Exception("Check has already run.")
         try:
             proc = subprocess.run(
@@ -53,3 +63,5 @@ class Check:
             raise RuntimeError(f"Command {self.Command} not found.")
         except subprocess.TimeoutExpired:
             raise RuntimeError("Timeout exceeded.")
+        self.ExitCode = proc.returncode
+        self.stderr = proc.stderr
diff --git a/pyproject.toml b/pyproject.toml
index 98e0fbf98172188c5af550aaf2b7d9d13b839dd8..4e121086ecbd23c5da5761005346767c15e8b184 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -32,6 +32,7 @@ requests = "^2.25.1"
 [tool.poetry.dev-dependencies]
 pre-commit = "^2.13.0"
 pyinstaller = "^4.3"
+pytest = "^6.2.4"
 
 [tool.poetry.scripts]
 mnpw = "mnpw:main"
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000000000000000000000000000000000000..e69de29bb2d1d6434b8b29ae775ad8c2e48c5391
diff --git a/tests/test_nagios.py b/tests/test_nagios.py
new file mode 100644
index 0000000000000000000000000000000000000000..2e5a883533cc23ae0e254e2e8d226255f78577db
--- /dev/null
+++ b/tests/test_nagios.py
@@ -0,0 +1,33 @@
+import pytest
+
+from mnpw import nagios
+
+
+@pytest.mark.parametrize(
+    "command,args,exit_code",
+    [
+        ("/bin/sh", ["-c", "exit 0"], nagios.NagiosCode.OK),
+        ("/bin/sh", ["-c", "exit 1"], nagios.NagiosCode.WARNING),
+        ("/bin/sh", ["-c", "exit 2"], nagios.NagiosCode.CRITICAL),
+        ("/bin/sh", ["-c", "exit 3"], nagios.NagiosCode.UNKNOWN),
+    ],
+)
+def test_check_exec(command, args, exit_code):
+    """Test the executation of checks."""
+    check = nagios.Check(command, args)
+    check.run()
+    assert check.ExitCode == exit_code
+
+
+def test_check_command_not_found():
+    """Test check with a nonexistant command."""
+    check = nagios.Check("/abcdef", [])
+    with pytest.raises(RuntimeError):
+        check.run()
+
+
+def test_check_timeout():
+    """Test check with a timed out command."""
+    check = nagios.Check("sleep", ["20"])
+    with pytest.raises(RuntimeError):
+        check.run(3)