= IBugLinkTarget Interface =

Launchpad includes Malone, the powerful bug tracker. One of the best
features of Malone is the ability to track a bug in multiple products
and/or packages. A bug can also be linked to other non-bug tracking
objects like questions, CVEs or specifications.

The IBugLinkTarget interface is used for that general purpose linking.
This file documents that interface and can be used to validate
implementation of this interface on a particular object. (This object is
made available through the 'target' variable which is defined outside of
this file, usually by a LaunchpadFunctionalTestCase. This instance
shouldn't have any bugs linked to it at the start of the test.)

    # Some parts of the IBugLinkTarget interface are only accessible
    # to a registered user.
    >>> login('no-priv@canonical.com')
    >>> from zope.interface.verify import verifyObject
    >>> from lp.bugs.interfaces.bug import IBugSet
    >>> from lp.bugs.interfaces.buglink import (
    ...     IBugLink,
    ...     IBugLinkTarget,
    ...     )

    >>> verifyObject(IBugLinkTarget, target)
    True

== linkBug() ==

    >>> bugset = getUtility(IBugSet)
    >>> bug1 = bugset.get(1)

The linkBug() method is used to link a bug to the target. It takes as
parameter the bug which should be linked. The method should return the
IBugLink that was created.

    >>> link1 = target.linkBug(bug1)

    >>> verifyObject(IBugLink, link1)
    True
    >>> link1.target == target
    True
    >>> link1.bug == bug1
    True

When the bug was already linked to the target, the existing link should
be used.

    >>> target.linkBug(bug1) == link1
    True

When a IBugLink is created, one IObjectCreatedEvent for the created
should be fired by the method.

    >>> from lp.testing.event import TestEventListener
    >>> from lazr.lifecycle.interfaces import (
    ...     IObjectCreatedEvent, IObjectDeletedEvent)
    >>> created_events = []
    >>> created_event_listener = TestEventListener(
    ...     IBugLink, IObjectCreatedEvent,
    ...     lambda object, event: created_events.append(event))

    >>> bug2 = bugset.get(2)
    >>> link2 = target.linkBug(bugset.get(2))
    >>> created_events[-1].object == link2
    True

Of course, if no new IBugLink is created, no events should be fired:

    >>> created_events = []
    >>> target.linkBug(bug2) == link2
    True
    >>> created_events
    []

Anonymous users cannot use linkBug():

    >>> login(ANONYMOUS)
    >>> target.linkBug(bug2)
    Traceback (most recent call last):
      ...
    Unauthorized...

A user can only link to a private bug if he is subscribed to the bug or
if he is an administrator:

    >>> login('no-priv@canonical.com')
    >>> private_bug = bugset.get(6)
    >>> private_bug.setPrivate(True, factory.makePerson())
    True
    >>> target.linkBug(private_bug)
    Traceback (most recent call last):
      ...
    Unauthorized...

    >>> login('foo.bar@canonical.com')
    >>> private_link = target.linkBug(private_bug)

== bugs ==

The list of bugs linked to the target should be available in the bugs
attributes:

    >>> [bug.id for bug in target.bugs]
    [1, 2, 6]

== bug_links ==

The IBugLink objects available on the target should be available in the
bug_links attribute:

    >>> [link.bug.id for link in target.bug_links]
    [1, 2, 6]

== unlinkBug() ==

The unlinkBug() method is used to remove a link between a bug and
the target.

This method is only available to registered users:

    >>> login(ANONYMOUS)
    >>> target.unlinkBug(bug2)
    Traceback (most recent call last):
      ...
    Unauthorized...

    >>> login('no-priv@canonical.com')

The method returns the linked object which was removed. It should also
send a IObjectDeletedEvent for the removed IBugLink:

    >>> deleted_events = []
    >>> deleted_event_listener = TestEventListener(
    ...     IBugLink, IObjectDeletedEvent,
    ...     lambda object, event: deleted_events.append(event))

    >>> target.unlinkBug(bug1) == link1
    True
    >>> deleted_events[-1].object == link1
    True

    >>> [bug.id for bug in target.bugs]
    [2, 6]

When the bug was not linked to the target, that method should return
None (and not trigger any events):

    >>> deleted_events = []
    >>> target.unlinkBug(bug1) is None
    True
    >>> deleted_events
    []

A user can only remove a link to a private bug if he is subscribed to
the bug or if he is an administrator.

    >>> target.unlinkBug(private_bug)
    Traceback (most recent call last):
      ...
    Unauthorized...

    >>> login('foo.bar@canonical.com')
    >>> target.unlinkBug(private_bug) == private_link
    True

== Cleanup ==

    # Unregister event listeners.
    >>> created_event_listener.unregister()
    >>> deleted_event_listener.unregister()