Add Unit Test for PooledDataSource

[hogimn]

I wrote several unit tests for PooledDataSource.

1. shouldBlockUntilConnectionIsAvailableInPooledDataSource

If program tries to get a connection beyond the number of dataSource.getPoolMaximumActiveConnections, it should be blocked.

2. PoppedConnectionShouldBeNotEqualToClosedConnection

The Popped Connection should be not equal to previously closed connection. When closing a connection, it should generate new connection and stash away it to idleConnections in PoolState.

3. shouldEnsureCorrectIdleConnectionCount

When closing a connection, the number of idle connection in idleConnections in PoolState increases by one, but not beyond dataSource.setPoolMaximumIdleConnections

4. connectionShouldBeAvailableAfterMaximumCheckoutTime

It is the test extending test 1. If program tries to get a connection beyond the number of dataSource.getPoolMaximumActiveConnections, program is blocked. But If time passes beyond dataSource.getPoolMaximumCheckoutTime, a connection should be available.

5. forceCloseAllShouldRemoveAllActiveAndIdleConnection

forceCloseAll should remove all active and idle connections.

Thank you.

[coveralls]

Coverage: 87.508% (+0.3%) from 87.183% when pulling 1640f1a on hogimn:test into 88ddca6 on mybatis:master.

[hazendaz]

@hogimn Thanks!