feat: add binary file helpers and file assertion utilities to test module

Co-authored-by: aider (openai/andrew/openrouter/qwen/qwen3-coder) <aider@aider.chat>

src/tests/common/test_helpers.rs

@@ -120,3 +120,27 @@ pub fn assert_files_equal(path1: &PathBuf, path2: &PathBuf) {
     let content2 = std::fs::read(path2).expect("Failed to read second file");
     assert_eq!(content1, content2, "Files {:?} and {:?} have different content", path1, path2);
 }
+
+/// Create a temporary file with binary content
+pub fn create_temp_file_with_binary_content(dir: &TempDir, filename: &str, content: &[u8]) -> PathBuf {
+    let file_path = dir.path().join(filename);
+    let mut file = File::create(&file_path).expect("Failed to create test file");
+    file.write_all(content).expect("Failed to write binary content to test file");
+    file_path
+}
+
+/// Get the size of a file
+pub fn get_file_size(file_path: &PathBuf) -> u64 {
+    let metadata = std::fs::metadata(file_path).expect("Failed to get file metadata");
+    metadata.len()
+}
+
+/// Assert that a file exists
+pub fn assert_file_exists(file_path: &PathBuf) {
+    assert!(file_path.exists(), "File {:?} does not exist", file_path);
+}
+
+/// Assert that a file does not exist
+pub fn assert_file_not_exists(file_path: &PathBuf) {
+    assert!(!file_path.exists(), "File {:?} should not exist but it does", file_path);
+}