Add conditions for ruby version < 3.1 to install mocha accordingly

Signed-off-by: Sonu Saha <sonu.saha@progress.com>

Gemfile

@@ -21,7 +21,9 @@ group :test do
   # but it's close enough to show the gempath handler can find a plugin
   # See test/unit/
   gem "train-test-fixture", path: "test/fixtures/plugins/train-test-fixture"
-  gem "mocha", "~> 2.1"
+  # Mocha ~1.1 is incompatible with minitest v5.19 and later
+  # More on the issue: https://github.com/freerange/mocha/issues/614
+  gem "mocha", (RUBY_VERSION < "3.1" ? "~> 1.1" : "~> 2.1")
 end
 
 if Gem.ruby_version >= Gem::Version.new("2.7.0")

test/unit/transports/ssh_test.rb

@@ -215,7 +215,7 @@
     end
 
     it "sets up a proxy when ssh proxy command is specified" do
-      mock = Minitest::Mock.new
+      mock = RUBY_VERSION < "3.1" ? MiniTest::Mock.new : Minitest::Mock.new
       mock.expect(:call, true) do |hostname, username, options|
         options[:proxy].is_a?(Net::SSH::Proxy::Command) &&
           "ssh root@127.0.0.1 -W %h:%p" == options[:proxy].command_line_template
@@ -384,7 +384,7 @@
       end
 
       it "sets up a proxy when ssh proxy command is specified" do
-        mock = Minitest::Mock.new
+        mock = RUBY_VERSION < "3.1" ? MiniTest::Mock.new : Minitest::Mock.new
         mock.expect(:call, true) do |hostname, username, options|
           options[:proxy].is_a?(Net::SSH::Proxy::Command) &&
             "ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no -o LogLevel=ERROR -o ForwardAgent=no -o IdentitiesOnly=yes -i #{conf[:key_files]} root@bastion_dummy -p 22 -W %h:%p" == options[:proxy].command_line_template