Refactor zones

#475

spec/models/dns/zone_spec.rb

@@ -10,4 +10,93 @@ RSpec.describe DNS::Zone do
       expect(described_class.origins).to eq('origins')
     end
   end
+
+  describe 'validation' do
+    let(:zone) { described_class.new }
+
+    required_attributes = %i[
+      origin
+      ttl
+      refresh
+      retry
+      expire
+      minimum_ttl
+      email
+      master_nameserver
+    ]
+
+    required_attributes.each do |attr_name|
+      it "rejects absent #{attr_name}", db: false do
+        zone.send("#{attr_name}=", nil)
+        zone.validate
+        expect(zone.errors).to have_key(attr_name)
+      end
+    end
+
+    integer_attributes = %i[
+      ttl
+      refresh
+      retry
+      expire
+      minimum_ttl
+    ]
+
+    integer_attributes.each do |attr_name|
+      it "rejects non-integer #{attr_name}", db: false do
+        zone.send("#{attr_name}=", 'test')
+        zone.validate
+        expect(zone.errors).to have_key(attr_name)
+      end
+
+      it "accepts integer #{attr_name}", db: false do
+        zone.send("#{attr_name}=", '1')
+        zone.validate
+        expect(zone.errors).to_not have_key(attr_name)
+      end
+    end
+  end
+
+  describe '#used?', db: false do
+    let!(:zone) { described_class.new }
+
+    context 'when domain uses zone' do
+      before :example do
+        allow(Domain).to receive(:uses_zone?).and_return(true)
+      end
+
+      specify { expect(zone).to be_used }
+    end
+
+    context 'when domain does not use zone' do
+      before :example do
+        allow(Domain).to receive(:uses_zone?).and_return(false)
+      end
+
+      specify { expect(zone).to_not be_used }
+    end
+  end
+
+  describe 'deletion', settings: false do
+    let!(:zone) { create(:zone) }
+
+    context 'when zone is unused' do
+      before :example do
+        allow(zone).to receive(:used?).and_return(false)
+      end
+
+      it 'is allowed' do
+        expect { zone.destroy }.to change { described_class.count }.from(1).to(0)
+      end
+    end
+
+    context 'when zone is used' do
+      before :example do
+        allow(zone).to receive(:used?).and_return(true)
+      end
+
+      it 'is disallowed' do
+        expect { zone.destroy }.to_not change { described_class.count }
+      end
+    end
+  end
 end