Fix issue with dastProfiles.branch GraphQL field

- Replace stub
- Update specs
- Add changelog entry

ee/app/models/dast/branch.rb

 # frozen_string_literal: true
 
 module Dast
-  Branch = Struct.new(:project) do
+  Branch = Struct.new(:profile) do
+    delegate :project, to: :profile
+
     def name
-      project.default_branch
+      profile.branch_name || project.default_branch
     end
 
     def exists
-      project.repository.branch_exists?(project.default_branch)
+      project.repository.branch_exists?(name)
     end
   end
 end

ee/app/models/dast/profile.rb

@@ -23,7 +23,7 @@ module Dast
     def branch
       return unless project.repository.exists?
 
-      Dast::Branch.new(project)
+      Dast::Branch.new(self)
     end
 
     private

ee/changelogs/unreleased/philipcunningham-fix-dast-branch-selection-issue.yml

+---
+title: Replace stubbed dastProfiles.branch GraphQL field
+merge_request: 56604
+author:
+type: fixed

ee/spec/graphql/types/dast/profile_type_spec.rb

@@ -31,7 +31,7 @@ RSpec.describe GitlabSchema.types['DastProfile'] do
 
     context 'when the feature flag is enabled' do
       it 'correctly resolves the field' do
-        expected_result = Dast::Branch.new(project)
+        expected_result = Dast::Branch.new(object)
 
         expect(resolve_field(:branch, object, current_user: user)).to eq(expected_result)
       end

ee/spec/models/dast/branch_spec.rb

@@ -3,11 +3,17 @@
 require 'spec_helper'
 
 RSpec.describe Dast::Branch do
-  let_it_be(:project) { create(:project) }
+  let_it_be(:dast_profile) { create(:dast_profile) }
 
-  subject { described_class.new(project) }
+  subject { described_class.new(dast_profile) }
 
-  describe 'instance methods' do
+  describe '#project' do
+    it 'delegates to profile.project' do
+      expect(subject.project).to eq(dast_profile.project)
+    end
+  end
+
+  context 'when profile.branch_name is nil' do
     context 'when the associated project does not have a repository' do
       describe '#name' do
         it 'returns nil' do
@@ -23,13 +29,41 @@ RSpec.describe Dast::Branch do
     end
 
     context 'when the associated project has a repository' do
-      let_it_be(:project) { create(:project, :repository) }
+      let_it_be(:dast_profile) { create(:dast_profile, project: create(:project, :repository)) }
 
       describe '#name' do
-        it 'returns the default_branch' do
-          expect(subject.name).to eq(project.default_branch)
+        it 'returns project.default_branch' do
+          expect(subject.name).to eq(subject.project.default_branch)
+        end
+      end
+
+      describe '#exists' do
+        it 'returns true' do
+          expect(subject.exists).to eq(true)
+        end
+      end
+    end
+  end
+
+  context 'when profile.branch_name is not nil' do
+    let_it_be(:dast_profile) { create(:dast_profile, branch_name: 'orphaned-branch') }
+
+    describe '#name' do
+      it 'returns profile.branch_name' do
+        expect(subject.name).to eq(dast_profile.branch_name)
+      end
+    end
+
+    context 'when the associated project does not have a repository' do
+      describe '#exists' do
+        it 'returns false' do
+          expect(subject.exists).to eq(false)
         end
       end
+    end
+
+    context 'when the associated branch has a repository and the branch exists' do
+      let_it_be(:dast_profile) { create(:dast_profile, project: create(:project, :repository), branch_name: 'orphaned-branch') }
 
       describe '#exists' do
         it 'returns true' do

ee/spec/policies/dast/branch_policy_spec.rb

@@ -4,6 +4,6 @@ require 'spec_helper'
 
 RSpec.describe Dast::BranchPolicy do
   it_behaves_like 'a dast on-demand scan policy' do
-    let_it_be(:record) { Dast::Branch.new(project) }
+    let_it_be(:record) { Dast::Branch.new(create(:dast_profile, project: project)) }
   end
 end