Add query test script and test mode

* Add a mode to test all metric queries

* Add a script to run query tests against different versions of
  PostgeSQL

* Add Docker elements for query testing

* Switch to using a --config flag when specifying the config file

* Fix some metric queries

* Allow the agent address to be configured

* Allow the sslmode connection parameter to be configured

src/pgmon.py

@@ -85,6 +85,8 @@ class MetricVersionError(Exception):
 
 # Default config settings
 default_config = {
+    # The address the agent binds to
+    "address": "127.0.0.1",
     # The port the agent listens on for requests
     "port": 5400,
     # Min PostgreSQL connection pool size (per database)
@@ -103,6 +105,8 @@ default_config = {
     "dbport": 5432,
     # Default database to connect to when none is specified for a metric
     "dbname": "postgres",
+    # SSL connection mode
+    "ssl_mode": "require",
     # Timeout for getting a connection slot from a pool
     "pool_slot_timeout": 5,
     # PostgreSQL connection timeout (seconds)
@@ -325,6 +329,7 @@ def get_pool(dbname):
             # lock
             if dbname not in connections:
                 log.info("Creating connection pool for: {}".format(dbname))
+                # Actually create the connection pool
                 connections[dbname] = ConnectionPool(
                     dbname,
                     int(config["min_pool_size"]),
@@ -334,7 +339,7 @@ def get_pool(dbname):
                     port=config["dbport"],
                     user=config["dbuser"],
                     connect_timeout=int(config["connect_timeout"]),
-                    sslmode="require",
+                    sslmode=config["ssl_mode"],
                 )
             # Clear the unhappy indicator if present
             unhappy_cooldown.pop(dbname, None)
@@ -382,10 +387,16 @@ def run_query_no_retry(pool, return_type, query, args):
                 res = curs.fetchall()
 
                 if return_type == "value":
+                    if len(res) == 0:
+                        return ""
                     return str(list(res[0].values())[0])
                 elif return_type == "row":
+                    if len(res) == 0:
+                        return "[]"
                     return json.dumps(res[0])
                 elif return_type == "column":
+                    if len(res) == 0:
+                        return "[]"
                     return json.dumps([list(r.values())[0] for r in res])
                 elif return_type == "set":
                     return json.dumps(res)
@@ -393,7 +404,7 @@ def run_query_no_retry(pool, return_type, query, args):
             dbname = pool.name
             if dbname in unhappy_cooldown:
                 raise UnhappyDBError()
-            elif conn.broken:
+            elif conn.closed != 0:
                 raise DisconnectedError()
             else:
                 raise
@@ -505,15 +516,14 @@ def test_queries():
     # We just use the default db for tests
     dbname = config["dbname"]
     # Loop through all defined metrics.
-    for metric_name in config["metrics"].keys():
-        # Get the actual metric definition
-        metric = metrics[metric_name]
+    for name, metric in config["metrics"].items():
         # If the metric has arguments to use while testing, grab those
         args = metric.get("test_args", {})
         # Run the query without the ability to retry.
-        res = sample_metric(dbname, metric_name, args, retry=False)
+        res = sample_metric(dbname, name, args, retry=False)
         # Compare the result to the provided sample results
         # TODO
+        print("{} -> {}".format(name, res))
     # Return the number of errors
     # TODO
     return 0
@@ -603,13 +613,16 @@ if __name__ == "__main__":
     )
 
     parser.add_argument(
-        "config_file",
+        "-c",
+        "--config_file",
         default="pgmon.yml",
         nargs="?",
         help="The config file to read (default: %(default)s)",
     )
 
-    parser.add_argument("test", action="store_true", help="Run query tests and exit")
+    parser.add_argument(
+        "-t", "--test", action="store_true", help="Run query tests and exit"
+    )
 
     args = parser.parse_args()
 
@@ -628,7 +641,7 @@ if __name__ == "__main__":
             sys.exit(0)
 
     # Set up the http server to receive requests
-    server_address = ("127.0.0.1", config["port"])
+    server_address = (config["address"], config["port"])
     httpd = ThreadingHTTPServer(server_address, SimpleHTTPRequestHandler)
 
     # Set up the signal handler