diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 1b6e31d9313505159d7075ac2d0b50e85f9fc42d..a34e44d7dfae7c16f8c2227215ee96723410fe5b 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -62,6 +62,7 @@ repos:
         additional_dependencies:
           - bandit
           - pyroma
+        exclude: ^tests/.*
 
   - repo: https://gitlab.com/pycqa/flake8.git
     rev: 3.9.2
diff --git a/mnpw/__init__.py b/mnpw/__init__.py
index 2b0fc95fbe445952b8267d7f392d5d82335bd7c5..abd3f75d0dd78603f40cfe50f2fed008b1b9be20 100644
--- a/mnpw/__init__.py
+++ b/mnpw/__init__.py
@@ -1,4 +1,5 @@
 """My Nagios plugin wrapper."""
+# pylint: disable=logging-fstring-interpolation
 __version__ = "0.1.0"
 
 import argparse
diff --git a/mnpw/nagios.py b/mnpw/nagios.py
index 01246b704725504688884bcab8006a95cd7ef0a3..a518d9b383e9c7a3fcbc2bd62e5610f3c05a5ac0 100644
--- a/mnpw/nagios.py
+++ b/mnpw/nagios.py
@@ -1,11 +1,14 @@
 """Nagios check implementation.
 
 Based on the specification from
-https://assets.nagios.com/downloads/nagioscore/docs/nagioscore/3/en/pluginapi.html"""
+https://assets.nagios.com/downloads/nagioscore/docs/nagioscore/3/en/pluginapi.html
+"""
+# pylint: disable=logging-fstring-interpolation
 
+import collections
 import enum
 import logging
-import subprocess
+import subprocess  # nosec
 
 DEFAULT_TIMEOUT = 10  # In seconds.
 
@@ -19,7 +22,13 @@ class NagiosCode(enum.IntEnum):
     UNKNOWN = 3
 
 
+PerfData = collections.namedtuple(
+    "PerfData", ["name", "value", "unit", "warning", "critical", "min", "max"]
+)
+
+
 class Check:
+    # pylint: disable=invalid-name
     """Nagios check using a plugin."""
 
     Command = None
@@ -32,7 +41,7 @@ class Check:
     stderr = None
     _stdout = None
 
-    def __init__(self, command, args):
+    def __init__(self, command, args=None):
         if not command:
             raise ValueError("Command is empty.")
         self.Command = command
@@ -55,7 +64,7 @@ class Check:
         ] + self.Arguments
         logging.info(f"Running command {_cmd}.")
         try:
-            proc = subprocess.run(
+            proc = subprocess.run(  # nosec
                 [
                     self.Command,
                 ]
diff --git a/tests/test_nagios.py b/tests/test_nagios.py
index 2e5a883533cc23ae0e254e2e8d226255f78577db..2483c6e3d5c8356c14a4682812e3f7d3287a493c 100644
--- a/tests/test_nagios.py
+++ b/tests/test_nagios.py
@@ -1,7 +1,24 @@
+import subprocess
+import unittest.mock
+
 import pytest
 
 from mnpw import nagios
 
+OUTPUT_1 = """DISK OK - free space: / 3326 MB (56%);"""
+OUTPUT_2 = (
+    """ DISK OK - free space: / 3326 MB (56%); | /=2643MB;5948;5958;0;5968"""
+)
+OUTPUT_3 = """\
+DISK OK - free space: / 3326 MB (56%); | /=2643MB;5948;5958;0;5968
+/ 15272 MB (77%);
+/boot 68 MB (69%);
+/home 69357 MB (27%);
+/var/log 819 MB (84%); | /boot=68MB;88;93;0;98
+/home=69357MB;253404;253409;0;253414
+/var/log=818MB;970;975;0;980
+"""
+
 
 @pytest.mark.parametrize(
     "command,args,exit_code",
@@ -30,4 +47,48 @@ def test_check_timeout():
     """Test check with a timed out command."""
     check = nagios.Check("sleep", ["20"])
     with pytest.raises(RuntimeError):
-        check.run(3)
+        check.run(timeout=3)
+
+
+def _mock_run(*args, **kwargs):
+    """Mock subprocess' run."""
+    return unittest.mock.patch.object(
+        nagios.subprocess,
+        "run",
+        *args,
+        **kwargs,
+    )
+
+
+@pytest.mark.parametrize(
+    "exception",
+    [
+        FileNotFoundError,
+        subprocess.TimeoutExpired(cmd="true", timeout=nagios.DEFAULT_TIMEOUT),
+    ],
+)
+def test_check_exceptions(exception):
+    """Test handling of subprocess' run exceptions.
+    See
+    https://docs.python.org/3/library/subprocess.html?highlight=popen#subprocess.SubprocessError
+    """
+    check = nagios.Check("true")
+    with _mock_run(side_effect=exception), pytest.raises(RuntimeError):
+        check.run()
+
+
+@pytest.mark.parametrize("output", [OUTPUT_1, OUTPUT_2, OUTPUT_3])
+def test_output_parsing(output):
+    """Test parsing of plugin output."""
+    check = nagios.Check("true")
+    proc = subprocess.CompletedProcess(
+        [
+            "true",
+        ],
+        0,
+        output,
+        "",
+    )
+    with _mock_run(return_value=proc):
+        check.run()
+        # TODO: validate something.