Getting error, "ORA-02020: too many database links in use", when testing several database links. (4334688)

Getting error "ORA-02020: too many database links in use" when testing many database links at the same time.

The error can also happen from running a query that accesses many db links. 

Steps to reproduce the issue:

1. Open Schema Browser
2. Select "Database Links"
3. Select a several Database Links  (more than 4)
4. Right-click and select "Test Database Links"
5. The error "ORA-02020" might appear

The current session has exceeded the INIT.ORA open_links maximum.
It is possible to check the value of this parameter by going to  Database | Administer | Oracle Parameters.

WORKAROUND 1:
  
1. Select only N database links (where N is the value of  the parameter open_links). 
2. Test these Database links. 
3. Disconnect from the database and select other N database links. 
4. Repeat the steps above until all the database links are tested. 
  
WORKAROUND 2:

Increase the value of the INIT.ORA parameter open_links (Note: this will require a reboot of the database).