is it a good practice that a developer test their own code?

Are you sure that a developer has code in the first place? Isn’t the code owned by the team, and shouldn’t the need to establish joint accountability determine who does what?

 Ricardo the short answer would be everyone owns quality. Test Strategy is a team decision.

Are you trying to influence the teams test strategy? Is the teams test strategy failing the them?

Sort of an ambiguous question.

I think it is okay to test their own code through unit tests but I would encourage building an environment that has frequent peer code reviews and a dedicated QE writing automated test cases. 

@Ian

I totally agree Ian, I actually trying to change the mindset of the team to be accountable for the sprint backlog towards achieving a sprint goal rather than being owners of single PBIs. (Work in progress)

@Mad

My team is compose with 7 developers and 2 testers (They focus on blackbox level). There is a bottleneck with testing activities. what I am trying to do is to encourage developers do testing as well at black box level. 

But developers claim that that another person should do the testing at black box level different from the person that do the implementation....  (I think this is another reflection of the lack of accountability in the team which I am trying to change)

@Anuj

I think I need to do more on this area

But developers claim that that another person should do the testing at black box level different from the person that do the implementation.... 

That may indeed be desirable, but why can't that person be another developer?