Redefine user roles with their role in a study group

spec/models/external_user_spec.rb

@@ -36,4 +36,10 @@ describe ExternalUser do
       expect(build(:external_user).teacher?).to be false
     end
   end
+
+  describe 'external_user has no current_study_group_id' do
+    it 'defaults to being a learner' do
+      expect(build(:external_user).learner?).to be true
+    end
+  end
 end

spec/models/internal_user_spec.rb

@@ -63,13 +63,9 @@ describe InternalUser do
     end
   end
 
-  it 'validates the domain of the role' do
-    user.update(role: 'Foo')
-    expect(user.errors[:role]).to be_present
-  end
-
-  it 'validates the presence of a role' do
-    expect(user.errors[:role]).to be_present
+  it 'validates the presence of the platform_admin flag' do
+    user.update(platform_admin: nil)
+    expect(user.errors[:platform_admin]).to be_present
   end
 
   describe '#admin?' do