Testing that hghave does not crash when checking features

  $ hghave --test-features 2>/dev/null

Testing hghave extensibility for third party tools

  $ cat > hghaveaddon.py <<EOF

  > import hghave

  > @hghave.check("custom", "custom hghave feature")

  > def has_custom():

  >     return True

  > EOF

(invocation via run-tests.py)

  $ cat > test-hghaveaddon.t <<EOF

  > #require custom

  >   $ echo foo

  >   foo

  > EOF

  $ run-tests.py $HGTEST_RUN_TESTS_PURE test-hghaveaddon.t

  .

(invocation via command line)

  $ unset TESTDIR

  $ hghave custom

(terminate with exit code 2 at failure of importing hghaveaddon.py)

  $ rm hghaveaddon.*

  $ cat > hghaveaddon.py <<EOF

  > importing this file should cause syntax error

  > EOF

  $ hghave custom

  failed to import hghaveaddon.py from '.': invalid syntax (hghaveaddon.py, line 1)

  [2]