diff --git a/doc/plugins.md b/doc/plugins.md
index e1845a7..95124f4 100644
--- a/doc/plugins.md
+++ b/doc/plugins.md
@@ -82,14 +82,17 @@ may occur multiple times):
   - The `label` attribute describes the output. Example:
 
     ```xml
-    <command label="host_data_source_list">/opt/xensource/bin/xe host-data-source-list host=$(/opt/xensource/bin/xe pool-list params=master --minimal)</command>
+    <command label="host_data_source_list">/opt/xensource/bin/xe host-data-source-list
+    host=$(/opt/xensource/bin/xe pool-list params=master --minimal)</command>
     ```
 
 ### Example `stuff.xml` file from the `xapi` bugtool Plugin
 
 ```xml
 <collect>
-<command label="sr_data_source_list">/opt/xensource/bin/xe sr-list --minimal | tr , '\n' | xargs --verbose -n 1 -I {} /opt/xensource/bin/xe sr-data-source-list uuid={} 2>&amp;1</command>
+<command label="sr_data_source_list">/opt/xensource/bin/xe sr-list --minimal |
+   tr , '\n' | xargs --verbose -n 1 -I {} /opt/xensource/bin/xe sr-data-source-list
+   uuid={} 2>&amp;1</command>
 <files>/etc/stunnel/xapi.conf</files>
 <list>/var/lib/corosync</list>
 <list recursive="false">/etc/xen/scripts</list>
diff --git a/tests/unit/conftest.py b/tests/unit/conftest.py
index 91aa17c..a4dcfa4 100644
--- a/tests/unit/conftest.py
+++ b/tests/unit/conftest.py
@@ -176,3 +176,22 @@ def isolated_bugtool(bugtool_log):
     os.chmod(".", 0o777)  # nosec # restore write permissions (for cleanup)
 
     # upon return, bugtool_log continues with its cleanup
+
+
+@pytest.fixture(scope="function")
+def bugtool_fixture(isolated_bugtool):
+    """
+    Fixture that wraps isolated_bugtool and restores its state after each test.
+    """
+
+    # Assert that isolated_bugtool is pristine and we have a clean state to start:
+    assert isolated_bugtool.data == {}
+    assert isolated_bugtool.entries is None
+
+    yield isolated_bugtool  # runs the test case in the read-only directory
+
+    # Restore isolated_bugtool to its pristine state:
+    isolated_bugtool.data = {}
+    isolated_bugtool.entries = None
+
+    # upon return, isolated_bugtool continues with its cleanup
diff --git a/tests/unit/test_cmd_output.py b/tests/unit/test_cmd_output.py
new file mode 100644
index 0000000..fa3bad1
--- /dev/null
+++ b/tests/unit/test_cmd_output.py
@@ -0,0 +1,110 @@
+"""tests/unit/test_cmd_output.py: Unit-Test bugtool.cmd_output()"""
+
+
+def test_cmd_output_mismatching_cap(bugtool_fixture):
+    """Assert that mismatching cap causes no extension of bugtool.data:"""
+
+    # Prepare that mismatching cap causes no output in bugtool.data:
+    bugtool_fixture.entries = [bugtool_fixture.CAP_PAM]
+
+    # Act
+    bugtool_fixture.cmd_output(bugtool_fixture.CAP_XENSERVER_LOGS, ["/bin/sh"])
+
+    # Assert that the command is not added to data
+    assert bugtool_fixture.data == {}
+
+
+def check_cmd_output_data(bugtool, command, label=None, filter_func=None):
+    """
+    Assert that cmd_output() stores the expected command in bugtool.data
+    It works by setting bugtool.data and bugtool.entries to fixed values
+    and asserting the expected bugtool.data after the check.
+
+    Use this function only with bugtool_fixture which saves and restores
+    the original values of these variables to avoid affecting other test cases.
+    """
+
+    # Prepare
+    bugtool.entries = [bugtool.CAP_PAM]
+    bugtool.data = {}
+
+    # Act
+    bugtool.cmd_output(bugtool.entries[0], command, label, filter=filter_func)
+
+    # Assert
+    assert bugtool.data == {
+        label
+        or command: {
+            "filter": filter_func,
+            "cap": bugtool.entries[0],
+            "cmd_args": command,
+        }
+    }
+
+
+def test_cmd_output_command(bugtool_fixture):
+    """Test how cmd_output() handles a command which can be found"""
+
+    check_cmd_output_data(bugtool_fixture, "pwd --version")
+
+
+def test_cmd_output_command_label(bugtool_fixture):
+    """Test how cmd_output() handles a command which can be found with a label"""
+
+    check_cmd_output_data(bugtool_fixture, "pwd --version", "label")
+
+
+def test_cmd_output_missing_command(bugtool_fixture):
+    """Test how cmd_output() handles a missing command"""
+
+    check_cmd_output_data(bugtool_fixture, "/missing-cmd arg")
+
+
+def test_cmd_output_missing_command_with_label(bugtool_fixture):
+    """Test how cmd_output() handles a missing command with a label"""
+
+    check_cmd_output_data(bugtool_fixture, "/missing-cmd arg", "label")
+
+
+def test_cmd_output_multiple_calls(bugtool_fixture):
+    """Assert the cumulative effect of multiple cmd_output() calls."""
+
+    # Prepare
+    #
+    cap1 = bugtool_fixture.CAP_OEM
+    cap2 = bugtool_fixture.CAP_PAM
+    bugtool_fixture.entries = [cap1, cap2]
+
+    def mock_filter():
+        """No-op mock filter used in tests for asserting it in bugtool_fixture.data"""
+
+    # Act
+    #
+    cmd1 = ["/usr/bin/pwd", "--version"]
+    cmd2 = ["/missing-cmd", "arg1", "arg2"]
+    bugtool_fixture.cmd_output("not_an_activated_capability", cmd1)
+    bugtool_fixture.cmd_output(cap1, [cmd1[0]], filter=mock_filter)
+    bugtool_fixture.cmd_output(cap1, cmd1)
+    bugtool_fixture.cmd_output(cap2, cmd2)
+
+    # Assert
+    #
+    assert bugtool_fixture.data == {
+        "pwd": {
+            "cap": cap1,
+            "cmd_args": ["/usr/bin/pwd"],
+            "filter": mock_filter,
+        },
+        # At the moment, we also add commands which are missing on the system to data
+        "missing-cmd arg1 arg2": {
+            "cap": cap2,
+            "cmd_args": cmd2,
+            "filter": None,
+        },
+        # Uses command as string without path as key when no label is set
+        "pwd --version": {
+            "cap": cap1,
+            "cmd_args": cmd1,
+            "filter": None,
+        },
+    }