Add step and API to add whole lines to a file

Due to how multi-line string literals work in Gherkin, it is easy to
accidentally have fewer newlines than intended when building up a file
using append_to_file.

To mitigate this while still allowing building up files without inserted
newlines, this change introduces a new API method #append_lines_to_file and
a corresponding step definition, that will ensure a newline is present
between the original content and the added content.

features/03_testing_frameworks/cucumber/steps/filesystem/append_to_file.feature

@@ -5,8 +5,8 @@ Feature: Append content to file
   Background:
     Given I use a fixture named "cli-app"
 
-  Scenario: Append to a existing file
-    Given a file named "features/non-existence.feature" with:
+  Scenario: Append to an existing file
+    Given a file named "features/appending.feature" with:
     """
     Feature: Existence
       Scenario: Existence
@@ -26,6 +26,28 @@ Feature: Append content to file
     When I run `cucumber`
     Then the features should all pass
 
+  Scenario: Append whole lines to a existing file
+    Given a file named "features/appending.feature" with:
+    """
+    Feature: Existence
+      Scenario: Existence
+        Given a file named "foo/bar/example.txt" with:
+        \"\"\"
+        hello world
+        \"\"\"
+        When I append the following lines to "foo/bar/example.txt":
+        \"\"\"
+        this was appended
+        \"\"\"
+        Then the file named "foo/bar/example.txt" should contain:
+        \"\"\"
+        hello world
+        this was appended
+        \"\"\"
+    """
+    When I run `cucumber`
+    Then the features should all pass
+
   Scenario: Append to a non-existing file
     Given a file named "features/non-existence.feature" with:
     """

lib/aruba/api/filesystem.rb

@@ -330,6 +330,24 @@ def append_to_file(file_name, file_content)
         File.open(file_name, 'a') { |f| f << file_content }
       end
 
+      # Append lines to a (text) file. This will make sure a newline is present
+      # between the old content and the new.
+      #
+      # @param [String] file_name
+      #   The name of the file to be used
+      #
+      # @param [String] file_content
+      #   The lines which should be appended to file
+      def append_lines_to_file(file_name, file_content)
+        file_name = expand_path(file_name)
+
+        last = File.open(file_name) { |f| f.seek(-3, IO::SEEK_END); f.read }
+        File.open(file_name, 'a') do |f|
+          f << "\n" unless last.end_with? "\n"
+          f << file_content
+        end
+      end
+
       # Create a directory in current directory
       #
       # @param [String] directory_name

lib/aruba/cucumber/file.rb

@@ -68,6 +68,10 @@
   append_to_file(file_name, file_content)
 end
 
+When(/^I append the following lines to "([^"]*)":$/) do |file_name, file_content|
+  append_lines_to_file(file_name, file_content)
+end
+
 When(/^I append to "([^"]*)" with "([^"]*)"$/) do |file_name, file_content|
   append_to_file(file_name, file_content)
 end

spec/aruba/api/filesystem_spec.rb

@@ -4,6 +4,23 @@
 RSpec.describe Aruba::Api::Filesystem do
   include_context 'uses aruba API'
 
+  describe '#append_lines_to_file' do
+    let(:path) { @file_path }
+    let(:name) { @file_name }
+
+    it "inserts a newline if existing file does not end in one" do
+      Aruba.platform.write_file(path, "foo\nbar")
+      append_lines_to_file(name, "baz")
+      expect(File.read(path)).to eq "foo\nbar\nbaz"
+    end
+
+    it "does not insert a newline if the existing file ends in one" do
+      Aruba.platform.write_file(path, "foo\nbar\n")
+      append_lines_to_file(name, "baz")
+      expect(File.read(path)).to eq "foo\nbar\nbaz"
+    end
+  end
+
   describe '#all_paths' do
     let(:name) { @file_name }
     let(:path) { @file_path }