Add SentryIssuesFinder and spec

app/finders/sentry_issues_finder.rb

+# frozen_string_literal: true
+
+class SentryIssuesFinder
+  def initialize(project, current_user = nil)
+    @project = project
+    @current_user = current_user
+  end
+
+  def find_by_identifier(identifier)
+    return unless Ability.allowed?(@current_user, :read_sentry_issue, @project)
+
+    sentry_issue = SentryIssue.for_identifier(identifier).first
+
+    return unless sentry_issue && sentry_issue.issue.project == @project
+
+    sentry_issue
+  end
+end

spec/finders/sentry_issues_finder_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe SentryIssuesFinder do
+  let(:user)       { create(:user) }
+  let(:project)    { create(:project, :repository) }
+  let(:issue) { create(:issue, project: project) }
+  let(:sentry_issue) { create(:sentry_issue, issue: issue) }
+
+  let(:finder) { described_class.new(project, user) }
+
+  describe '#find_by_identifier' do
+    let(:identifier) { sentry_issue.sentry_issue_identifier }
+
+    subject { finder.find_by_identifier(identifier) }
+
+    context 'when the user is not part of the project' do
+      it 'returns no sentry issues' do
+        is_expected.to eq(nil)
+      end
+    end
+
+    context 'when the user is a project developer' do
+      before do
+        project.add_developer(user)
+      end
+
+      it 'returns the matching sentry issue' do
+        expect(subject).to eq(sentry_issue)
+      end
+
+      context 'when identifier is incorrect is false' do
+        let(:identifier) { 1234 }
+
+        it 'does not return a sentry issue' do
+          expect(subject).to eq(nil)
+        end
+      end
+
+      context 'when accessing another projects identifier' do
+        let(:second_project) { create(:project) }
+        let(:second_issue) { create(:issue, project: second_project) }
+        let(:second_sentry_issue) { create(:sentry_issue, issue: second_issue) }
+
+        let(:identifier) { second_sentry_issue.sentry_issue_identifier }
+
+        it 'does not return a sentry issue' do
+          expect(subject).to eq(nil)
+        end
+      end
+    end
+  end
+end