Diffy test

Author: Malax

Gemfile

@@ -5,6 +5,7 @@ source 'https://rubygems.org'
 ruby '>= 3.2', '< 3.5'
 
 group :test, :development do
+  gem 'diffy', '~> 3.4'
   gem 'heroku_hatchet'
   gem 'java-properties'
   # Work around https://github.com/excon/excon/issues/860

Gemfile.lock

@@ -4,6 +4,7 @@ GEM
     ast (2.4.3)
     base64 (0.3.0)
     diff-lcs (1.6.2)
+    diffy (3.4.4)
     erubis (2.7.0)
     excon (1.2.7)
       logger
@@ -82,6 +83,7 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
+  diffy (~> 3.4)
   heroku_hatchet
   java-properties
   logger

test/spec/versions_spec.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require_relative 'spec_helper'
+require 'diffy'
 
 RSpec.describe 'Maven buildpack' do
   it 'runs Maven wrapper instead of installing Maven when possible' do
@@ -34,6 +35,18 @@
       add_to_system_properties('maven.version', UNKNOWN_MAVEN_VERSION)
     end
 
+    a = <<~OUTPUT
+      remote: -----> Installing Maven #{UNKNOWN_MAVEN_VERSION}...
+      remote:  
+      remote:  !     ERROR: You have defined an unsupported Maven version in the system.properties file.
+      remote:  !     
+      remote:  !     The default supported version is #{DEFAULT_MAVEN_VERSION}
+      remote:  
+      remote:  !     Push rejected, failed to compile Java app.
+    OUTPUT
+
+    warn(Diffy::Diff.new(clean_output(app.output), a).to_s(:html))
+
     app.deploy do
       expect(clean_output(app.output)).to include(<<~OUTPUT)
         remote: -----> Installing Maven #{UNKNOWN_MAVEN_VERSION}...