tests: add a basic test to check config precedence

Signed-off-by: Andrea Terzolo <andreaterzolo3@gmail.com>

unit_tests/CMakeLists.txt

@@ -27,10 +27,18 @@ FetchContent_MakeAvailable(googletest)
 file(GLOB_RECURSE ENGINE_TESTS ${CMAKE_CURRENT_SOURCE_DIR}/engine/*.cpp)
 file(GLOB_RECURSE FALCO_TESTS ${CMAKE_CURRENT_SOURCE_DIR}/falco/*.cpp)
 
+# Create a libscap_test_var.h file with some variables used by our tests
+# for example the kmod path or the bpf path.
+configure_file (
+    "${CMAKE_CURRENT_SOURCE_DIR}/falco_test_var.h.in"
+    "${CMAKE_CURRENT_BINARY_DIR}/falco_test_var.h"
+)
+
 set(FALCO_UNIT_TESTS_SOURCES
   "${ENGINE_TESTS}"
   falco/test_configuration.cpp
   falco/app/actions/test_select_event_sources.cpp
+  falco/app/actions/test_load_config.cpp
 )
 
 if (CMAKE_SYSTEM_NAME MATCHES "Linux")
@@ -45,6 +53,7 @@ set(FALCO_UNIT_TESTS_INCLUDES
     ${CMAKE_SOURCE_DIR}/userspace
     ${CMAKE_BINARY_DIR}/userspace/falco # we need it to include indirectly `config_falco.h` file
     ${CMAKE_SOURCE_DIR}/userspace/engine # we need it to include indirectly `falco_common.h` file
+	"${CMAKE_CURRENT_BINARY_DIR}" # we need it to include `falco_test_var.h`
 )
 
 set(FALCO_UNIT_TESTS_DEPENDENCIES

unit_tests/falco/app/actions/test_load_config.cpp

@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: Apache-2.0
+/*
+Copyright (C) 2023 The Falco Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless ASSERTd by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+#include "app_action_helpers.h"
+#include "falco_test_var.h"
+
+TEST(ActionLoadConfig, check_depracated_falco_038_configs)
+{
+	auto action = falco::app::actions::load_config;
+
+	// todo!: remove in 0.38.0 since we don't have anymore any precedence
+	{
+		falco::app::state s;
+		s.options.conf_filename = ENGINE_SELECTION_TEST_CONFIG;
+		EXPECT_ACTION_OK(action(s));
+		EXPECT_EQ(s.config->m_modern_ebpf.m_buf_size_preset, 5);
+		EXPECT_TRUE(s.config->m_modern_ebpf.m_drop_failed_exit);
+		EXPECT_EQ(s.config->m_modern_ebpf.m_cpus_for_each_syscall_buffer, 3);
+	}
+}

unit_tests/falco/test_configs/test_engine_selection_precedence.yaml

@@ -0,0 +1,51 @@
+# SPDX-License-Identifier: Apache-2.0
+#
+# Copyright (C) 2023 The Falco Authors.
+#
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+################
+# Falco engine #
+################
+
+engine:
+  kind: modern-ebpf
+  kmod:
+    buf_size_preset: 4
+    drop_failed_exit: false
+  ebpf:
+    probe: /path/to/probe.o
+    buf_size_preset: 4 
+    drop_failed_exit: false
+  modern-ebpf:
+    cpus_for_each_syscall_buffer: 1
+    buf_size_preset: 5 # This should win over the other config
+    drop_failed_exit: false
+  replay:
+    trace_file: /path/to/file.scap
+  gvisor:
+    config: /path/to/gvisor.yaml
+    root: /gvisor/root
+
+#######################################
+# Falco performance tuning (advanced) #
+#######################################
+
+syscall_buf_size_preset: 4
+
+syscall_drop_failed_exit: true # This should win over the other config
+
+modern_bpf:
+  cpus_for_each_syscall_buffer: 3 # Should win this 3 over the 1 in the other config

unit_tests/falco_test_var.h.in

@@ -0,0 +1,3 @@
+#pragma once
+
+#define ENGINE_SELECTION_TEST_CONFIG "${CMAKE_SOURCE_DIR}/unit_tests/falco/test_configs/test_engine_selection_precedence.yaml"