Let’s take a ‘pot shot’ that might help, shall we?
The process of changing to the testing branch can usually be achieved with the following commands (as can be found in the Switching Branches wiki article ‘Changing to another branch’);
The recommended series of commands:
1. Change to the testing branch:
sudo pacman-mirrors --api --set-branch testing
2. Rebuild the mirrorlist:
sudo pacman-mirrors --fasttrack
3. Perform a full system update:
This allows your system to fully sync with the testing branch.
sudo pacman -Syu
However you seem to be having difficulty with dependencies, so I might suggest a slight deviation from the norm; 
A suggested series of commands:
1. Change to the testing branch:
sudo pacman-mirrors --api --set-branch testing
2. Rebuild the mirrorlist:
This time we limit mirrors to those available to your continent (optional).
sudo pacman-mirrors --continent
3. Perform a full system update:
This allows your system to fully sync with the testing branch.
sudo pacman -Syyuu
Notice the change in the update command.
This variation allows downgrading packages (as needed) and may be helpful to resolve your dependency issues in the process.
I note that most of this information has already been given (in varying shapes and forms) by other Members.
This post basically consolidates that into a more coherent and readable format.
I trust it may be useful. 
Regards.
See also:
- pacman (Manjaro Wiki)
- pacman-mirrors (Manjaro Wiki)
- pacman (Arch Wiki)