Folding tests (elixir-editors#453)

* basic folding test

* move matcher over, extract buffer method, example dsl

* support folding on lower lines, give failure message

* add a few examples

Author: schnittchen

spec/folding/basic_spec.rb

@@ -0,0 +1,58 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe 'Basic folding' do
+  def self.it_folds_lines(content, lines, tags = nil)
+    it("folds #{lines} lines on \n#{content}", tags) do
+      expect(content).to fold_lines(lines, tags)
+    end
+  end
+
+  it_folds_lines(<<~EOF, 2)
+  defmodule M do
+  end
+  "not in fold"
+  EOF
+
+  it_folds_lines(<<~EOF, 4)
+  defmodule M do
+    def some_func do
+    end
+  end
+  "not in fold"
+  EOF
+
+  it_folds_lines(<<~EOF, 2, on_line: 2)
+  defmodule M do
+    def some_func do
+    end
+  end
+  "not in fold"
+  EOF
+
+  it_folds_lines(<<~EOF, 2)
+  if true do
+  end
+  "not in fold"
+  EOF
+
+  it_folds_lines(<<~EOF, 3, on_line: 3)
+  if true do
+    nil
+  else
+    nil
+  end
+  "not in fold"
+  EOF
+
+  it_folds_lines(<<~EOF, 5, skip: "broken")
+  if true do
+    nil
+  else
+    nil
+  end
+  "not in fold"
+  EOF
+end
+

spec/spec_helper.rb

@@ -61,6 +61,18 @@ def syntax(content, pattern)
     syngroups.gsub!(/["'\[\]]/, '').split(', ')
   end
 
+  def fold_and_delete(content, opts)
+    start_line = opts[:on_line]
+    with_file content do
+      @vim.command("set foldmethod=syntax")
+
+      @vim.normal("zO")
+      @vim.normal("#{start_line}G")
+      @vim.normal("zc")
+      @vim.normal("dd")
+    end
+  end
+
   private
 
   def with_file(content = nil)
@@ -193,6 +205,31 @@ def self.new
   end
 end
 
+RSpec::Matchers.define :fold_lines do |lines, opts|
+  buffer = Buffer.new(VIM, :ex)
+  opts ||= {}
+  start_line = opts[:on_line] ||= 1
+
+  after = nil
+
+  match do |code|
+    after = buffer.fold_and_delete(code, opts)
+
+    code.lines.count - after.lines.count == lines
+  end
+
+  failure_message do |code|
+    <<~EOF
+    expected
+    #{code}
+    to fold #{lines} lines at line #{start_line},
+    but after folding at line #{start_line} and deleting a line I got
+    #{after}
+    back
+    EOF
+  end
+end
+
 Vimrunner::RSpec.configure do |config|
   config.reuse_server = true