Add self to group via signal message

Value Statement

• AS AN activist trying to grow a list of rapid response volunteers
• I WANT volunteers to be able to add themselves
• SO THAT I don't get slowed down by adding them myself

Acceptance Criteria

GIVEN a command channel with phone number +1-555-555-5555

• AND and a relay channel with phone number +1-666-666-6666 and name #red-alert
• AND a user alice, who is an admin of the relay channel
• AND a user bobby, who is new (not a member of any channel)
• WHEN bob sends a message to +1-555-555-5555 that says join #red-alert
• THEN bob will be added to the subscribers of #red-alert
• AND THEN bob will receive a signal message from +1-666... saying "you have been added to the #red-alert group."

GIVEN the same conditions above

• WHEN bob sends a message to 555... that does not start with the word join
• THEN she receives an appropriate error message and usage instructions (eg: sorry: we did not understand that command. valid commands include...)

GIVEN the same conditions as above

• WHEN bobby sends a message to join a non-existent channel
• THEN she should receive an error message saying that channel dos not exist (do NOT list channels that do exist)

GIVEN the same conditions as above

• AND bob has successfully added themselves to the #red-alert channel
• WHEN alice sends a message to +1-666..., both alice and bob will receive a message from that number

GIVEN the same conditions as above

• WHEN alice sends a (second) "join" message to +1-666...
• THEN she will receive a message from +1-666... saying "whoops! you already subscribed to #red-alert"
• AND WHEN alice sends a message to the channel, bob does not see the message

Out of Scope

• implementing a "join message" with instructions on how to either leave (#22 (closed)) or ask for help (#14 (closed))
• implementing a "you do not have permission to send messages to this group" message when a user tries to send a message to a group they are not an admin of (ticket needed)