Simplify model validation specs for AccountMigration (#32494)

spec/models/account_migration_spec.rb

@@ -9,8 +9,8 @@ RSpec.describe AccountMigration do
     end
   end
 
-  describe 'validations' do
+  describe 'Validations' do
-    subject { described_class.new(account: source_account, acct: target_acct) }
+    subject { Fabricate.build :account_migration, account: source_account }
 
     let(:source_account) { Fabricate(:account) }
     let(:target_acct)    { target_account.acct }
@@ -26,9 +26,7 @@ RSpec.describe AccountMigration do
         allow(service_double).to receive(:call).with(target_acct, anything).and_return(target_account)
       end
 
-      it 'passes validations' do
+      it { is_expected.to allow_value(target_account.acct).for(:acct) }
-        expect(subject).to be_valid
-      end
     end
 
     context 'with unresolvable account' do
@@ -40,17 +38,13 @@ RSpec.describe AccountMigration do
         allow(service_double).to receive(:call).with(target_acct, anything).and_return(nil)
       end
 
-      it 'has errors on acct field' do
+      it { is_expected.to_not allow_value(target_acct).for(:acct) }
-        expect(subject).to model_have_error_on_field(:acct)
-      end
     end
 
     context 'with a space in the domain part' do
       let(:target_acct) { 'target@remote. org' }
 
-      it 'has errors on acct field' do
+      it { is_expected.to_not allow_value(target_acct).for(:acct) }
-        expect(subject).to model_have_error_on_field(:acct)
-      end
     end
   end
 end