2 files changed, 59 insertions, 0 deletions
diff --git a/test/rubygems/test_gem_commands_build_command.rb b/test/rubygems/test_gem_commands_build_command.rb
index 0c511b2f08..50c447e2eb 100644
--- a/test/rubygems/test_gem_commands_build_command.rb
+++ b/test/rubygems/test_gem_commands_build_command.rb
@@ -457,4 +457,36 @@ class TestGemCommandsBuildCommand < Gem::TestCase
     assert_match(/INFO:  Your expired cert will be located at: .+\Wgem-public_cert\.pem\.expired\.[0-9]+/, output.shift)
   end
 
+  def test_build_is_reproducible
+    epoch = ENV["SOURCE_DATE_EPOCH"]
+    new_epoch = Time.now.to_i.to_s
+    ENV["SOURCE_DATE_EPOCH"] = new_epoch
+
+    gem_file = File.basename(@gem.cache_file)
+
+    gemspec_file = File.join(@tempdir, @gem.spec_name)
+    File.write(gemspec_file, @gem.to_ruby)
+    @cmd.options[:args] = [gemspec_file]
+
+    util_test_build_gem @gem
+
+    build1_contents = File.read(gem_file)
+
+    # Guarantee the time has changed.
+    sleep 1 if Time.now.to_i == new_epoch
+
+    ENV["SOURCE_DATE_EPOCH"] = new_epoch
+
+    @ui = Gem::MockGemUi.new
+    @cmd.options[:args] = [gemspec_file]
+
+    util_test_build_gem @gem
+
+    build2_contents = File.read(gem_file)
+
+    assert_equal build1_contents, build2_contents
+  ensure
+    ENV["SOURCE_DATE_EPOCH"] = epoch
+  end
+
 end
diff --git a/test/rubygems/test_gem_package.rb b/test/rubygems/test_gem_package.rb
index f2f712ebe0..a282e0cc5f 100644
--- a/test/rubygems/test_gem_package.rb
+++ b/test/rubygems/test_gem_package.rb
@@ -2,6 +2,7 @@
 # frozen_string_literal: true
 
 require 'rubygems/package/tar_test_case'
+require 'digest'
 
 class TestGemPackage < Gem::Package::TarTestCase
 
@@ -123,6 +124,32 @@ class TestGemPackage < Gem::Package::TarTestCase
     ENV["SOURCE_DATE_EPOCH"] = epoch
   end
 
+  def test_build_time_source_date_epoch_automatically_set
+    epoch = ENV["SOURCE_DATE_EPOCH"]
+    ENV["SOURCE_DATE_EPOCH"] = nil
+
+    start_time = Time.now.utc.to_i
+
+    spec = Gem::Specification.new 'build', '1'
+    spec.summary = 'build'
+    spec.authors = 'build'
+    spec.files = ['lib/code.rb']
+    spec.rubygems_version = Gem::Version.new '0'
+
+    package = Gem::Package.new spec.file_name
+
+    end_time = Time.now.utc.to_i
+
+    assert package.build_time.is_a?(Time)
+
+    build_time = package.build_time.to_i
+
+    assert(start_time <= build_time)
+    assert(build_time <= end_time)
+  ensure
+    ENV["SOURCE_DATE_EPOCH"] = epoch
+  end
+
   def test_add_files
     spec = Gem::Specification.new
     spec.files = %w[lib/code.rb lib/empty]