Embed integration tests into pytest.

tests/test_command_line.py

@@ -0,0 +1,23 @@
+"""
+Test command line commands.
+"""
+from subprocess import PIPE, Popen
+
+__author__ = "Sergey Vartanov"
+__email__ = "me@enzet.ru"
+
+
+def error_run(arguments: list[str], message: bytes) -> None:
+    """Run command that should fail and check error message."""
+    p = Popen(["map-machine"] + arguments, stderr=PIPE)
+    _, error = p.communicate()
+    assert p.returncode != 0
+    assert error == message
+
+
+def run(arguments: list[str], message: bytes) -> None:
+    """Run command that should fail and check error message."""
+    p = Popen(["map-machine"] + arguments, stderr=PIPE)
+    _, error = p.communicate()
+    assert p.returncode == 0
+    assert error == message