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/meta_plugin/digest_tests.rs

@@ -1 +1,47 @@
-// Meta plugin digest tests
+#[cfg(test)]
+mod tests {
+    use keep::meta_plugin::digest::*;
+    use keep::meta_plugin::MetaPlugin;
+    use std::io::Write;
+
+    #[test]
+    fn test_digest_sha256_meta_plugin() {
+        let mut plugin = DigestSha256MetaPlugin::new("test_digest".to_string());
+        
+        assert_eq!(plugin.meta_name(), "test_digest");
+        assert!(plugin.is_internal());
+        
+        // Creating a writer should work
+        let writer_result = plugin.create();
+        assert!(writer_result.is_ok());
+        
+        // Writing some data
+        let mut writer = writer_result.unwrap();
+        let write_result = writer.write(b"test data");
+        assert!(write_result.is_ok());
+    }
+
+    #[test]
+    fn test_read_time_meta_plugin() {
+        let mut plugin = ReadTimeMetaPlugin::new("read_time_test".to_string());
+        
+        assert_eq!(plugin.meta_name(), "read_time_test");
+        assert!(plugin.is_internal());
+        
+        // Creating a writer should work
+        let writer_result = plugin.create();
+        assert!(writer_result.is_ok());
+    }
+
+    #[test]
+    fn test_read_rate_meta_plugin() {
+        let mut plugin = ReadRateMetaPlugin::new("read_rate_test".to_string());
+        
+        assert_eq!(plugin.meta_name(), "read_rate_test");
+        assert!(plugin.is_internal());
+        
+        // Creating a writer should work
+        let writer_result = plugin.create();
+        assert!(writer_result.is_ok());
+    }
+}