feat: implement comprehensive tests for all modules including database, meta plugins, compression engines, modes, server auth, and utilities to complete Phase 2

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

src/tests/common/is_binary_tests.rs

@@ -1 +1,39 @@
-// Common is_binary tests
+#[cfg(test)]
+mod tests {
+    use keep::common::is_binary::calculate_printable_ratio;
+
+    #[test]
+    fn test_calculate_printable_ratio_text() {
+        let text_data = b"Hello, World! This is plain text.\nWith newlines and spaces.";
+        let ratio = calculate_printable_ratio(text_data);
+        
+        // Text data should have high printable ratio
+        assert!(ratio > 0.8);
+    }
+
+    #[test]
+    fn test_calculate_printable_ratio_binary() {
+        let binary_data = b"\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09";
+        let ratio = calculate_printable_ratio(binary_data);
+        
+        // Binary data should have low printable ratio
+        assert!(ratio < 0.5);
+    }
+
+    #[test]
+    fn test_calculate_printable_ratio_mixed() {
+        let mixed_data = b"Text\xff\xfe\xfdMore text\x00\x01";
+        let ratio = calculate_printable_ratio(mixed_data);
+        
+        // Mixed data should have medium printable ratio
+        assert!(ratio > 0.3 && ratio < 0.8);
+    }
+
+    #[test]
+    fn test_calculate_printable_ratio_empty() {
+        let empty_data = b"";
+        // Empty data would cause division by zero, but the function should handle it
+        // Note: This test might need adjustment based on actual implementation
+        let _ = calculate_printable_ratio(empty_data);
+    }
+}