Updated for Angular >=8 CLI For one component, use the following command: 

ng generate component --skipTests=true component-name
For a single project, change or add the following in your angular.json: 

{ 
  "projects": {
    "{PROJECT_NAME}": {
      "schematics": {
        "@schematics/angular:component": {
          "skipTests": true
        }
      }
    }
  }
}
For a global setting for all your projects, change or add the following in your angular.json: 

{ 
  "schematics": {
    "@schematics/angular:component": {
      "skipTests": true
    }
  }
}
Or by using the command line 

ng config schematics.@schematics/angular:component.skipTests true
For Angular < 8 Inside your angular-cli.json set the spec.component parameter to false: 

{
   ...
   "defaults" : {
       ...
       "spec": {
           ...
           "component": false
       }
   }
}
or use the --spec=false option during creation 

ng generate component --spec=false component-name