Original implementation to allow users to subscribe to labels

1. Allow subscribing (the current user) to a label

- Refactor the `Subscription` coffeescript class
  - The main change is that it accepts a container, and conducts all
    DOM queries within its scope. We need this because the labels
    page has multiple instances of `Subscription` on the same page.

2. Creating an issue or MR with labels notifies users subscribed to those labels

- Label `has_many` subscribers through subscriptions.

3. Adding a label to an issue or MR notifies users subscribed to those labels

- This only applies to subscribers of the label that has just been
  added, not all labels for the issue.

1 files changed, 13 insertions, 0 deletions

diff --git a/spec/support/email_helpers.rb b/spec/support/email_helpers.rb
new file mode 100644
index 00000000000..a85ab22ce36
--- /dev/null
+++ b/spec/support/email_helpers.rb
@@ -0,0 +1,13 @@
+module EmailHelpers
+  def sent_to_user?(user)
+    ActionMailer::Base.deliveries.map(&:to).flatten.count(user.email) == 1
+  end
+
+  def should_email(user)
+    expect(sent_to_user?(user)).to be_truthy
+  end
+
+  def should_not_email(user)
+    expect(sent_to_user?(user)).to be_falsey
+  end
+end