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require 'spec_helper'
describe Parslet::Atoms::Lookahead do
include Parslet
describe 'negative lookahead' do
it "influences the error tree" do
parser = str('f').absent? >> str('b')
cause = catch_failed_parse { parser.parse('f') }
cause.ascii_tree.should == "Failed to match sequence (!'f' 'b') at line 1 char 1.\n`- Input should not start with 'f' at line 1 char 1.\n"
end
end
describe 'positive lookahead' do
it "influences the error tree" do
parser = str('f').present? >> str('b')
cause = catch_failed_parse { parser.parse('b') }
cause.ascii_tree.should == "Failed to match sequence (&'f' 'b') at line 1 char 1.\n`- Input should start with 'f' at line 1 char 1.\n"
end
end
end
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