Fix MySQL tests and disposal (#774)

* Don't create the connection in Dispose: this avoids creating a SQLConnection simply to Dispose it.
* Run MySQL tests against the open MySqlConnection: 'connection' is a protected variable in the TestBase class that is a SQL Server connection, not a MySQL connection.
* Skip broken MySQL tests: as per issue #295, setting "AllowZeroDateTime=True" in the connection string causes an InvalidCastException in SqlMapper.

Dapper.Tests/Providers/MySQLTests.cs

@@ -26,9 +26,9 @@ public class MySQLTests : TestBase
         [FactMySql]
         public void DapperEnumValue_Mysql()
         {
-            using (var connection = GetMySqlConnection())
+            using (var conn = GetMySqlConnection())
             {
-                Common.DapperEnumValue(connection);
+                Common.DapperEnumValue(conn);
             }
         }
 
@@ -77,7 +77,7 @@ public void Issue295_NullableDateTime_MySql_Default()
         {
             using (var conn = GetMySqlConnection(true, false, false))
             {
-                Common.TestDateTime(connection);
+                Common.TestDateTime(conn);
             }
         }
 
@@ -86,25 +86,25 @@ public void Issue295_NullableDateTime_MySql_ConvertZeroDatetime()
         {
             using (var conn = GetMySqlConnection(true, true, false))
             {
-                Common.TestDateTime(connection);
+                Common.TestDateTime(conn);
             }
         }
 
-        [FactMySql]
+        [FactMySql(Skip = "See https://github.com/StackExchange/Dapper/issues/295, AllowZeroDateTime=True is not supported")]
         public void Issue295_NullableDateTime_MySql_AllowZeroDatetime()
         {
             using (var conn = GetMySqlConnection(true, false, true))
             {
-                Common.TestDateTime(connection);
+                Common.TestDateTime(conn);
             }
         }
 
-        [FactMySql]
+        [FactMySql(Skip = "See https://github.com/StackExchange/Dapper/issues/295, AllowZeroDateTime=True is not supported")]
         public void Issue295_NullableDateTime_MySql_ConvertAllowZeroDatetime()
         {
             using (var conn = GetMySqlConnection(true, true, true))
             {
-                Common.TestDateTime(connection);
+                Common.TestDateTime(conn);
             }
         }
 
@@ -186,4 +186,4 @@ static FactMySqlAttribute()
         }
     }
 }
-#endif
\ No newline at end of file
+#endif

Dapper.Tests/TestBase.cs

@@ -78,7 +78,7 @@ static TestBase()
 
         public void Dispose()
         {
-            connection?.Dispose();
+            _connection?.Dispose();
         }
     }
 }