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# frozen_string_literal: true
RSpec.shared_examples 'metrics sampler' do |env_prefix|
context 'when sampling interval is passed explicitly' do
subject(:sampler) { described_class.new(interval: 42, logger: double) }
specify { expect(sampler.interval).to eq(42) }
end
context 'when sampling interval is passed through the environment' do
subject(:sampler) { described_class.new(logger: double) }
before do
stub_env("#{env_prefix}_INTERVAL_SECONDS", '42')
end
specify { expect(sampler.interval).to eq(42) }
end
context 'when no sampling interval is passed anywhere' do
subject(:sampler) { described_class.new(logger: double) }
it 'uses the hardcoded default' do
expect(sampler.interval).to eq(described_class::DEFAULT_SAMPLING_INTERVAL_SECONDS)
end
end
describe '#start' do
include WaitHelpers
subject(:sampler) { described_class.new(interval: 0.1) }
it 'calls the sample method on the sampler thread' do
sampling_threads = []
expect(sampler).to receive(:sample).at_least(:once) { sampling_threads << Thread.current }
sampler.start
wait_for('sampler has sampled', max_wait_time: 3) { sampling_threads.any? }
expect(sampling_threads.first.name).to eq(sampler.thread_name)
sampler.stop
end
context 'with warmup set to true' do
subject(:sampler) { described_class.new(interval: 0.1, warmup: true) }
it 'calls the sample method first on the caller thread' do
sampling_threads = []
current_thread = Thread.current
# Instead of sampling, we're keeping track of which thread the sampling happened on.
# We want the first sample to be on the spec thread, which would mean a blocking sample
# before the actual sampler thread starts.
expect(sampler).to receive(:sample).at_least(:once) { sampling_threads << Thread.current }
sampler.start
wait_for('sampler has sampled', max_wait_time: 3) { sampling_threads.size == 2 }
expect(sampling_threads.first).to be(current_thread)
expect(sampling_threads.last.name).to eq(sampler.thread_name)
sampler.stop
end
end
end
describe '#safe_sample' do
let(:logger) { Logger.new(File::NULL) }
subject(:sampler) { described_class.new(logger: logger) }
it 'calls #sample once' do
expect(sampler).to receive(:sample)
sampler.safe_sample
end
context 'when sampling fails with error' do
before do
expect(sampler).to receive(:sample).and_raise "something failed"
end
it 'recovers from errors' do
expect { sampler.safe_sample }.not_to raise_error
end
context 'with logger' do
let(:logger) { double('logger') }
it 'logs errors' do
expect(logger).to receive(:warn).with(an_instance_of(String))
expect { sampler.safe_sample }.not_to raise_error
end
end
end
end
end
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