Extract User#parsed_roles method

I'm planning to introduce another role-related predicate method in a
subsequent commit. Extracting this method first will make that change
easier.

I'm pretty convinced the call to `#to_s` was made redundant when the
safe navigation operator was introduced in this commit [1]. However,
I suppose it's theoretically possible for the parsed JSON returned from
`HydraPublicApiClient.fetch_oauth_user` via `User.from_token` to contain
non-String values, so I'm going to leave it in place for now.

[1]: 9a1fdb1

Author: floehopper

app/models/user.rb

@@ -51,7 +51,11 @@ def student?
   end
 
   def admin?
-    (roles&.to_s&.split(',')&.map(&:strip) || []).include?('editor-admin')
+    parsed_roles.include?('editor-admin')
+  end
+
+  def parsed_roles
+    roles&.to_s&.split(',')&.map(&:strip) || []
   end
 
   def ==(other)

spec/models/user_spec.rb

@@ -277,24 +277,36 @@
     end
   end
 
-  describe '#admin?' do
-    it 'returns true if the user has the editor-admin role in Hydra' do
-      user = build(:user, roles: 'editor-admin')
-      expect(user).to be_admin
+  describe '#parsed_roles' do
+    it 'returns array of role names when roles is set to comma-separated string' do
+      user = build(:user, roles: 'role-1,role-2')
+      expect(user.parsed_roles).to eq(%w[role-1 role-2])
     end
 
-    it 'returns false if the user does not have the editor-admin role in Hydra' do
-      user = build(:user, roles: 'another-editor-admin')
-      expect(user).not_to be_admin
+    it 'strips leading & trailing spaces from role names' do
+      user = build(:user, roles: ' role-1 , role-2 ')
+      expect(user.parsed_roles).to eq(%w[role-1 role-2])
     end
 
-    it 'returns false if roles are empty in Hydra' do
+    it 'returns empty array when roles is set to empty string' do
       user = build(:user, roles: '')
-      expect(user).not_to be_admin
+      expect(user.parsed_roles).to eq([])
     end
 
-    it 'returns false if roles are nil in Hydra' do
+    it 'returns empty array when roles is set to nil' do
       user = build(:user, roles: nil)
+      expect(user.parsed_roles).to eq([])
+    end
+  end
+
+  describe '#admin?' do
+    it 'returns true if the user has the editor-admin role in Hydra' do
+      user = build(:user, roles: 'editor-admin')
+      expect(user).to be_admin
+    end
+
+    it 'returns false if the user does not have the editor-admin role in Hydra' do
+      user = build(:user, roles: 'another-editor-admin')
       expect(user).not_to be_admin
     end
   end