Added missing test for the exists rule pattern matching limit

spec/lib/gitlab/ci/build/rules/rule/clause/exists_spec.rb

@@ -4,11 +4,24 @@ require 'spec_helper'
 
 describe Gitlab::Ci::Build::Rules::Rule::Clause::Exists do
   describe '#satisfied_by?' do
+    let(:pipeline) { build(:ci_pipeline, project: project, sha: project.repository.head_commit.sha) }
+
+    subject { described_class.new(globs).satisfied_by?(pipeline, nil) }
+
     it_behaves_like 'a glob matching rule' do
       let(:project) { create(:project, :custom_repo, files: files) }
-      let(:pipeline) { build(:ci_pipeline, project: project, sha: project.repository.head_commit.sha) }
+    end
+
+    context 'after pattern comparision limit is reached' do
+      let(:globs) { ['*definitely_not_a_matching_glob*'] }
+      let(:project) { create(:project, :repository) }
+
+      before do
+        stub_const('Gitlab::Ci::Build::Rules::Rule::Clause::Exists::MAX_PATTERN_COMPARISONS', 2)
+        expect(File).to receive(:fnmatch?).exactly(2).times.and_call_original
+      end
 
-      subject { described_class.new(globs).satisfied_by?(pipeline, nil) }
+      it { is_expected.to be_truthy }
     end
   end
 end