Run benchmark only when ENV['BENCHMARK'] == 'yes'

[aycabta]

The test suite of RDoc has a benchmark test. The benchmark test is run when ENV['BENCHMARK'] is set, but Rakefile locks ENV['BENCHMARK'] is 'yes'. Nobody can change whether to run benchmark. This won't serve the purpose.

This Pull Request serves new behavior:

• Run benchmark test only when ENV['BENCHMARK'] is 'yes'
• Rakefile sets ENV['BENCHMARK'] as 'yes' only when ENV['BENCHMARK'] isn't set

The benchmark test runs with rake. The benchmark test doesn't run with BENCHMARK=no rake.

This is for avoidance of dependence on CI circumstances.

[zzak]

Can we skip this test too?
https://github.com/rdoc/rdoc/blob/master/test/test_rdoc_context.rb#L410

I think there is only one benchmark in the whole suite:
https://github.com/rdoc/rdoc/search?utf8=%E2%9C%93&q=bench&type=

[aycabta]

MiniTest runs assert_performance_* only if require 'minitest/benchmark' evaluated. This Pull Request makes control of run/skip assert_performance_linear what is just one benchmark test in RDoc by require 'minitest/benchmark' or not, over ENV['BENCHMARK']

[aycabta]

README.txt of RDoc 4.x describes those at "Benchmark" section.

[aycabta]

@zzak I'll explicitly renpond your question.

I think there is only one benchmark in the whole suite

Yes, I think the same way.

Can we skip this test too?

Yes, BENCHMARK=no rake skips the only one benchmark by this Pull Request.