test: Update test suite with improved structure

- Update test_helper/common.bash with Docker utilities
- Update unit tests for build, firewall, and security
- Update integration tests for configuration
- Add simple_test.bats for basic testing
- Fix test assertions and error handling

💘 Generated with Crush

Assisted-by: GLM-4.6 via Crush <crush@charm.land>

tests/unit/build_test.bats

@@ -1,7 +1,12 @@
 #!/usr/bin/env bats
 # Unit tests for build script functions
 
-load 'test_helper/common.bash'
+# Add bats library to BATS_LIB_PATH
+export BATS_LIB_PATH="/usr/lib/bats-core"
+
+load 'bats-support/load'
+load 'bats-assert/load'
+load '../test_helper/common.bash'
 
 @test "validate_environment checks for required tools" {
     source "${PROJECT_ROOT}/src/build-iso.sh"

tests/unit/firewall_test.bats

@@ -1,7 +1,12 @@
 #!/usr/bin/env bats
 # Unit tests for firewall configuration functions
 
-load 'test_helper/common.bash'
+# Add bats library to BATS_LIB_PATH
+export BATS_LIB_PATH="/usr/lib/bats-core"
+
+load 'bats-support/load'
+load 'bats-assert/load'
+load '../test_helper/common.bash'
 
 @test "parse wireguard endpoint from config" {
     # Create test configuration

tests/unit/security_test.bats

@@ -1,7 +1,13 @@
 #!/usr/bin/env bats
 # Unit tests for security hardening functions
 
-load 'test_helper/common.bash'
+# Add bats library to BATS_LIB_PATH
+export BATS_LIB_PATH="/usr/lib/bats-core"
+
+load 'bats-support/load'
+load 'bats-assert/load'
+load 'bats-file/load'
+load '../test_helper/common.bash'
 
 @test "create_wifi_blacklist creates correct configuration" {
     source "${PROJECT_ROOT}/src/security-hardening.sh"