There is an option in .angular-cli.json to disable the automatic creating of *.spec files e.g. for components, see json schema.
This is a really nice feature because personally (this is just my opinion) testing the components might not be the thing that really worth it in a fast growing project.
However sometimes I would like to have an option to generate / recreate the corresponding *.spec file for an already existing component / service / pipe / whatsoever.
Is that possible using some command line call?
Created a feature request, let's see how it goes...
Currently Angular CLI does not provide this functionality and it is not clear how and when it will be possible to manage it in official way.
However, here is a library "ngx-spec" that generates the spec based on Angular CLI spec presets.
If you are using vsCode the authors of ngx-spec recomend using this extension https://github.com/cyrilletuzi/vscode-angular-schematics