Improve PrometheusAlert EE validation

ee/spec/models/prometheus_alert_spec.rb

 require 'spec_helper'
 
 describe PrometheusAlert do
-  let(:metric) { create(:prometheus_metric) }
+  set(:project) { build(:project) }
+  let(:metric) { build(:prometheus_metric) }
 
   describe 'associations' do
     it { is_expected.to belong_to(:project) }
     it { is_expected.to belong_to(:environment) }
   end
 
+  describe 'project validations' do
+    let(:environment) { build(:environment, project: project) }
+    let(:metric) { build(:prometheus_metric, project: project) }
+
+    subject do
+      build(:prometheus_alert, prometheus_metric: metric, environment: environment, project: project)
+    end
+
+    context 'when environment and metric belongs same project' do
+      it { is_expected.to be_valid }
+    end
+
+    context 'when environment belongs to different project' do
+      let(:environment) { build(:environment) }
+
+      it { is_expected.not_to be_valid }
+    end
+
+    context 'when metric belongs to different project' do
+      let(:metric) { build(:prometheus_metric) }
+
+      it { is_expected.not_to be_valid }
+    end
+
+    context 'when metric is common' do
+      let(:metric) { build(:prometheus_metric, :common) }
+
+      it { is_expected.to be_valid }
+    end
+  end
+
   describe '#full_query' do
-    it 'returns the concatenated query' do
+    before do
       subject.operator = "gt"
       subject.threshold = 1
-      subject.prometheus_metric_id = metric.id
+      subject.prometheus_metric = metric
+    end
 
+    it 'returns the concatenated query' do
       expect(subject.full_query).to eq("#{metric.query} > 1.0")
     end
   end
 
   describe '#to_param' do
-    it 'returns the params of the prometheus alert' do
+    before do
       subject.operator = "gt"
       subject.threshold = 1
-      subject.prometheus_metric_id = metric.id
+      subject.prometheus_metric = metric
+    end
 
-      alert_params = {
+    it 'returns the params of the prometheus alert' do
+      expect(subject.to_param).to eq(
         "alert" => metric.title,
         "expr" => "#{metric.query} > 1.0",
         "for" => "5m",
         "labels" => {
           "gitlab" => "hook",
           "gitlab_alert_id" => metric.id
-        }
-      }
-
-      expect(subject.to_param).to eq(alert_params)
+        })
     end
   end
 end