database: some debugs

src/database.js

@@ -57,6 +57,8 @@ async function initialize() {
     });
 
     gConnectionPool.on('connection', function (connection) {
+        debug('connected');
+
         // connection objects are re-used. so we have to attach to the event here (once) to prevent crash
         // note the pool also has an 'acquire' event but that is called whenever we do a getConnection()
         connection.on('error', (error) => debug(`Connection ${connection.threadId} error: ${error.message} ${error.code}`));
@@ -74,6 +76,7 @@ async function uninitialize() {
 
     gConnectionPool.end();
     gConnectionPool = null;
+    debug('connection closed');
 }
 
 async function clear() {
@@ -86,7 +89,7 @@ async function clear() {
 }
 
 async function query() {
-    assert.notStrictEqual(gConnectionPool, null);
+    assert.notStrictEqual(gConnectionPool, null, 'Database connection is already closed');
 
     return new Promise((resolve, reject) => {
         const args = Array.prototype.slice.call(arguments);