The prerequisite to have WcfTestClient is to have Windows Communication Foundation component installed. If WcfTestClient is missing, install it by modifying Visual Studio:
Control Panel > Apps & Features > Visual Studio (your version)
In Visual Studio Installer, click on Modify, choose Individual components tab and then select (see below screenshot):
? Windows Communication Foundation
Click on Modify and voilĂ , application will be on your disk.
If you want to use WcfTestClient with no Visual Studio, see answer(s) on: How can the Wcf Test Client be used without Visual Studio?