[autoscaler] Enforce CommandRunnerInterface abstractions (#10822)

Co-authored-by: root <root@ip-172-31-28-155.us-west-2.compute.internal>
Co-authored-by: Ameer Haj Ali <ameerhajali@Ameers-MacBook-Pro.local>

python/ray/tests/test_command_runner.py

@@ -1,7 +1,8 @@
 import pytest
 from ray.tests.test_autoscaler import MockProvider, MockProcessRunner
-from ray.autoscaler.command_runner import SSHCommandRunner, \
-    _with_environment_variables, DockerCommandRunner, KubernetesCommandRunner
+from ray.autoscaler.command_runner import CommandRunnerInterface, \
+    SSHCommandRunner, _with_environment_variables, DockerCommandRunner, \
+    KubernetesCommandRunner
 from ray.autoscaler.docker import DOCKER_MOUNT_PREFIX
 from getpass import getuser
 import hashlib
@@ -27,6 +28,33 @@ def test_environment_variable_encoder_dict():
     assert res == expected
 
 
+def test_command_runner_interface_abstraction_violation():
+    """Enforces the CommandRunnerInterface functions on the subclasses.
+
+    This is important to make sure the subclasses do not violate the
+    function abstractions. If you need to add a new function to one of
+    the CommandRunnerInterface subclasses, you have to add it to
+    CommandRunnerInterface and all of its subclasses.
+    """
+
+    cmd_runner_interface_public_functions = dir(CommandRunnerInterface)
+    allowed_public_interface_functions = {
+        func
+        for func in cmd_runner_interface_public_functions
+        if not func.startswith("_")
+    }
+    for subcls in [
+            SSHCommandRunner, DockerCommandRunner, KubernetesCommandRunner
+    ]:
+        subclass_available_functions = dir(subcls)
+        subclass_public_functions = {
+            func
+            for func in subclass_available_functions
+            if not func.startswith("_")
+        }
+        assert allowed_public_interface_functions == subclass_public_functions
+
+
 def test_ssh_command_runner():
     process_runner = MockProcessRunner()
     provider = MockProvider()