1 files changed, 41 insertions, 0 deletions
diff --git a/spec/lib/gitlab/ci/yaml_processor/dag_spec.rb b/spec/lib/gitlab/ci/yaml_processor/dag_spec.rb
new file mode 100644
index 00000000000..af1b43f6b01
--- /dev/null
+++ b/spec/lib/gitlab/ci/yaml_processor/dag_spec.rb
@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+require 'fast_spec_helper'
+
+RSpec.describe Gitlab::Ci::YamlProcessor::Dag do
+  let(:nodes) { {} }
+
+  subject(:result) { described_class.new(nodes).tsort }
+
+  context 'when it is a regular pipeline' do
+    let(:nodes) do
+      { 'job_c' => %w(job_b job_d), 'job_d' => %w(job_a), 'job_b' => %w(job_a), 'job_a' => %w() }
+    end
+
+    it 'returns ordered jobs' do
+      expect(result).to eq(%w(job_a job_b job_d job_c))
+    end
+  end
+
+  context 'when there is a circular dependency' do
+    let(:nodes) do
+      { 'job_a' => %w(job_c), 'job_b' => %w(job_a), 'job_c' => %w(job_b) }
+    end
+
+    it 'raises TSort::Cyclic' do
+      expect { result }.to raise_error(TSort::Cyclic, /topological sort failed/)
+    end
+  end
+
+  context 'when there is a missing job' do
+    let(:nodes) do
+      { 'job_a' => %w(job_d), 'job_b' => %w(job_a) }
+    end
+
+    it 'raises MissingNodeError' do
+      expect { result }.to raise_error(
+        Gitlab::Ci::YamlProcessor::Dag::MissingNodeError, 'node job_d is missing'
+      )
+    end
+  end
+end