Portify for Mac provides a way of transferring your Spotify playlists to Google Music: All Access, but is hampered by two things: difficult installation and legal ambiguity. In terms of installation, the app is offered as source files, which means it's up to you to compile and build it. As far as the legality of the app is concerned, it uses private APIs to do its job -- something which is frowned upon and may break the EULA.
Portify for Mac does not have an APP package right out of the box -- you have to build it yourself using developer tools, a complicated process, which instantly makes the app inaccessible to the majority of Mac users. Once the app is built and running, you are presented with a four-step setup process, which includes logging in to your Google and Spotify accounts. Note that if you use a two-factor authentication with Google, you will need to generate an app-specific password, as well as to have signed up for the Google Music: All Access service. After both credentials have been verified, you are presented with a list of your Spotify playlists from which you can select which to import. The transfer process takes only a few seconds.
Planning to switch to Google Music from Spotify and don't want to waste time compiling a new set of playlists? Consider using Portify for Mac, a good, albeit complicated app, but keep in mind that due to the use of private APIs, the app may stop working the moment either company makes a modification. If you're nervous about possibly breaking your license agreements, you shouldn't use this app.