Implement rspec TestEnvHelpers:

Allow use of our test environment, with a mocked remote and convenient
methods to write more concise expectations.

  #env, builds and returns a memoized test environment (with mocked
  remote)

  #output, returns env output as a string

  #remote_fs, returns env remote fs

  #expect_execution, setup a remote command execution expectation

spec/support/test_env_helpers.rb

@@ -0,0 +1,31 @@
+module TestEnvHelpers
+  require 'producer/core/testing'
+
+  def env
+    @_env ||= build_env
+  end
+
+  def output
+    env.output.string
+  end
+
+  def remote_fs
+    env.remote.fs
+  end
+
+  def expect_execution(command)
+    opts = { expected_from: caller.first }
+    RSpec::Mocks.expect_message(env.remote, :execute, opts).with(command)
+  end
+
+
+  private
+
+  def build_env
+    Producer::Core::Env.new(output: StringIO.new, remote: build_remote)
+  end
+
+  def build_remote
+    Producer::Core::Testing::MockRemote.new('some_host.test')
+  end
+end