kube: Don't crash w/o section_kube_{cpu,memory}

These sections can be missing during an upgrade (for example if
generated section goes from v1 to v2). Don't crash in this case,
just return an empty result.

Change-Id: I742f8f4ee0759f5a55a4326a0aaa83e1ee024c73

Author: relrod

packages/cmk-plugins/cmk/plugins/kube/agent_based/kube_cpu.py

@@ -59,7 +59,9 @@ def _check_kube_cpu(
     current_timestamp: float,
     host_value_store: MutableMapping[str, Any],
 ) -> CheckResult:
-    assert section_kube_cpu_resources is not None
+    if section_kube_cpu_resources is None:
+        return
+
     yield from check_resource(
         params,
         performance_cpu(

packages/cmk-plugins/cmk/plugins/kube/agent_based/kube_memory.py

@@ -57,7 +57,9 @@ def check_kube_memory(
     section_kube_memory_resources: Resources | None,
     section_kube_allocatable_memory_resource: AllocatableResource | None,
 ) -> CheckResult:
-    assert section_kube_memory_resources is not None
+    if section_kube_memory_resources is None:
+        return
+
     yield from check_resource(
         params,
         section_kube_performance_memory,

packages/cmk-plugins/tests/cmk/plugins/kube/agent_based/test_kube_cpu.py

@@ -9,7 +9,6 @@
 
 import itertools
 
-import pytest
 from polyfactory.factories.pydantic_factory import ModelFactory
 
 import cmk.plugins.kube.kube
@@ -67,13 +66,14 @@ def test_discovery() -> None:
 
 
 def test_check_if_no_resources() -> None:
-    """Crashing is expected, because section_kube_cpu is only missing, if data from the api
-    server missing."""
+    """
+    No results expected when section_kube_cpu is missing,
+    e.g. if the API server is unreachable or during upgrades.
+    """
     check_result = kube_cpu._check_kube_cpu(
         PARAMS, USAGE_SECTION, None, ALLOCATABLE_RESOURCE_SECTION, 1.0, {}
     )
-    with pytest.raises(AssertionError):
-        list(check_result)
+    assert list(check_result) == []
 
 
 def test_performance_cpu() -> None:

packages/cmk-plugins/tests/cmk/plugins/kube/agent_based/test_kube_memory.py

@@ -303,18 +303,22 @@ def test_check_kube_memory(
         ),
     ],
 )
-def test_crashes_if_no_resources(
+def test_no_results_if_no_resources(
     section_kube_performance_memory: PerformanceUsage | None,
 ) -> None:
-    with pytest.raises(AssertionError):
-        list(
-            check_kube_memory(
-                DEFAULT_PARAMS,
-                section_kube_performance_memory,
-                None,
-                AllocatableResource(context="node", value=35917989.0),
-            )
+    """
+    No results expected when section_kube_memory is missing,
+    e.g. if the API server is unreachable or during upgrades.
+    """
+    result = list(
+        check_kube_memory(
+            DEFAULT_PARAMS,
+            section_kube_performance_memory,
+            None,
+            AllocatableResource(context="node", value=35917989.0),
         )
+    )
+    assert result == []
 
 
 @pytest.mark.parametrize(