Make various trace methods take last_lines argument:

So that we could read last few lines rather than read
the entire file which could be huge.

1 files changed, 40 insertions, 0 deletions

diff --git a/spec/lib/gitlab/ci/trace_reader_spec.rb b/spec/lib/gitlab/ci/trace_reader_spec.rb
new file mode 100644
index 00000000000..f06d78694d6
--- /dev/null
+++ b/spec/lib/gitlab/ci/trace_reader_spec.rb
@@ -0,0 +1,40 @@
+require 'spec_helper'
+
+describe Gitlab::Ci::TraceReader do
+  let(:path) { __FILE__ }
+  let(:lines) { File.readlines(path) }
+  let(:bytesize) { lines.sum(&:bytesize) }
+
+  it 'returns last few lines' do
+    10.times do
+      subject = build_subject
+      last_lines = random_lines
+
+      expected = lines.last(last_lines).join
+
+      expect(subject.read(last_lines: last_lines)).to eq(expected)
+    end
+  end
+
+  it 'returns everything if trying to get too many lines' do
+    expect(build_subject.read(last_lines: lines.size * 2)).to eq(lines.join)
+  end
+
+  it 'raises an error if not passing an integer for last_lines' do
+    expect do
+      build_subject.read(last_lines: lines)
+    end.to raise_error(ArgumentError)
+  end
+
+  def random_lines
+    Random.rand(lines.size) + 1
+  end
+
+  def random_buffer
+    Random.rand(bytesize) + 1
+  end
+
+  def build_subject
+    described_class.new(__FILE__, buffer_size: random_buffer)
+  end
+end