Add main link to each phase of the budget

Co-authored-by: decabeza <alberto@decabeza.es>

spec/models/budget/phase_spec.rb

@@ -111,6 +111,29 @@ describe Budget::Phase do
         expect(informing_phase).to be_valid
       end
     end
+
+    describe "main_link_url" do
+      it "is not required if main_link_text is not provided" do
+        valid_budget = build(:budget, main_link_text: nil)
+
+        expect(valid_budget).to be_valid
+      end
+
+      it "is required if main_link_text is provided" do
+        invalid_budget = build(:budget, main_link_text: "link text")
+
+        expect(invalid_budget).not_to be_valid
+        expect(invalid_budget.errors.count).to be 1
+        expect(invalid_budget.errors[:main_link_url].count).to be 1
+        expect(invalid_budget.errors[:main_link_url].first).to eq "can't be blank"
+      end
+
+      it "is valid if main_link_text and main_link_url are both provided" do
+        budget = build(:budget, main_link_text: "link text", main_link_url: "https://consulproject.org")
+
+        expect(budget).to be_valid
+      end
+    end
   end
 
   describe "#save" do