MLIA-1037 Fix default backend validation

Add a check to see if the default backends are installed when no backend
is provided via CLI.

Change-Id: I27dd9f35cfeec187f44cba06915d1be5a3a052b5
Signed-off-by: Benjamin Klimczak <benjamin.klimczak@arm.com>

2 files changed, 29 insertions, 4 deletions

diff --git a/src/mlia/cli/command_validators.py b/src/mlia/cli/command_validators.py
index a0f5433..04e04b1 100644
--- a/src/mlia/cli/command_validators.py
+++ b/src/mlia/cli/command_validators.py
@@ -7,6 +7,7 @@ import argparse
 import logging
 import sys
 
+from mlia.backend.manager import get_available_backends
 from mlia.target.registry import default_backends
 from mlia.target.registry import get_target
 from mlia.target.registry import supported_backends
@@ -14,9 +15,7 @@ from mlia.target.registry import supported_backends
 logger = logging.getLogger(__name__)
 
 
-def validate_backend(
-    target_profile: str, backend: list[str] | None
-) -> list[str] | None:
+def validate_backend(target_profile: str, backend: list[str] | None) -> list[str]:
     """Validate backend with given target profile.
 
     This validator checks whether the given target-profile and backend are
@@ -26,7 +25,15 @@ def validate_backend(
     target = get_target(target_profile)
 
     if not backend:
-        return default_backends(target)
+        defaults = default_backends(target)
+        missing_backends = set(defaults)
+        missing_backends.difference_update(get_available_backends())
+        if missing_backends:
+            raise argparse.ArgumentError(
+                None,
+                f"The following default backends are not installed: {missing_backends}",
+            )
+        return defaults
 
     compatible_backends = list(map(normalize_string, supported_backends(target)))
     backends = {normalize_string(b): b for b in backend}
diff --git a/tests/test_cli_command_validators.py b/tests/test_cli_command_validators.py
index 1ac82db..e140749 100644
--- a/tests/test_cli_command_validators.py
+++ b/tests/test_cli_command_validators.py
@@ -5,6 +5,7 @@ from __future__ import annotations
 
 import argparse
 from contextlib import ExitStack
+from unittest.mock import MagicMock
 
 import pytest
 
@@ -160,3 +161,20 @@ def test_validate_backend(
 
     with exit_stack:
         assert validate_backend(input_target_profile, input_backends) == output_backends
+
+
+def test_validate_backend_default_available() -> None:
+    """Test default backend validation with available backend."""
+    backends = validate_backend("cortex-a", None)
+    assert backends
+    assert backends == ["armnn-tflite-delegate"]
+
+
+def test_validate_backend_default_unavailable(monkeypatch: pytest.MonkeyPatch) -> None:
+    """Test default backend validation with unavailable backend."""
+    monkeypatch.setattr(
+        "mlia.cli.command_validators.default_backends",
+        MagicMock(return_value=["UNKNOWN_BACKEND"]),
+    )
+    with pytest.raises(argparse.ArgumentError):
+        validate_backend("cortex-a", None)