Add ParserTestDriver

[cosmo0920]

Currently, fluentd does not have ParserTestDriver.
This PR adds this test driver.

Remaining tasks

• Frozen ParserTestDriver API
  • Decide whether to include utility methods such as str2time or not.
• Replace a few parser test cases with ParserTestDriver
• Documentations?

[repeatedly]

Could you replace one actual parser test with this driver?

[cosmo0920]

I try to replace TimeParser and SyslogParse test cases with ParserTestDriver.

[cosmo0920]

I've found that parser test driver in this commit cosmo0920@d5d0846 does not handle to instantiate RegexParser.
How do we abstract this parser with this test driver?

Ah, my understanding is wrong. In RegexParser#initialize, conf argument is optional...

[okkez]

I want to write parser test like following:

def test_multiline
  conf = %[
  <grok>
    pattern %{DATA:message1}\n
  </grok>
  <grok>
    pattern %{DATA:message2}\n
  </grok>
  ]
  text = <<TEXT
host1 message1
  message2
TEXT
  d = Fluent::Parser::TestDriver.new(Fluent::TextParser::MultilineGrokParser).configure(conf)
  d.parse(text) do |time, record|
     assert_equal(expected, record)
  end
end

This is same as other test drivers.

[repeatedly]

TimeParser itself is not a Parser plugin so I think supporting TimeParser API is not needed.

[cosmo0920]

Rebased. I removed a commit which replaces TimeParse test cases with ParserTestDriver.

[repeatedly]

@okkez How about this? If you ok, I will merge this patch.

[okkez]

How to use nested config_section and cnofig_param?
How about this?

But this is no tested.

def configure(conf)
  case conf
  when Fluent::Config::Element
    @config = conf
  when String
    io = StringIO.new(conf)
    @config = Cofig::Parser.parse(io, 'fluent.conf')
  when Hash
    @config = Config::Element.new('ROOT', '', conf, [])
  else
    raise "Unknown type... #{conf}"
  end
  @instance.configure(@config)
  self
end

[cosmo0920]

As a result of @okkez and I discussion, I added commits to drop TimeParser support in this test driver, to fix usage of Class.new, and to support string literal in #configure.

Could you review this PR again?

[repeatedly]

If there are no concerns from other developers, I will merge it.

[okkez]

Looks good to me 👍