Port custom/custom_dep to new test suite.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

cabal-install/tests/IntegrationTests/custom/custom_dep.sh

-. ./common.sh
-
-# On Travis OSX, Cabal shipped with GHC 7.8 does not work
-# with error "setup: /usr/bin/ar: permission denied"; see
-# also https://github.com/haskell/cabal/issues/3938
-# This is a hack to make the test not run in this case.
-if [ "$TRAVIS_OS_NAME" = "osx" ]; then
-    require_ghc_ge 710
-fi
-
-cd custom_dep
-cabal sandbox init
-cabal sandbox add-source custom
-cabal sandbox add-source client
-# Some care must be taken here: we want the Setup script
-# to build against GHC's bundled Cabal, but passing
-# --package-db=clear --package-db=global to cabal is
-# insufficient, as these flags are NOT respected when
-# building Setup scripts.  Changing HOME to a location
-# which definitely does not have a local .cabal
-# directory works, the environment variable propagates to GHC.
-HOME=`pwd` cabal install client

cabal-testsuite/PackageTests/CustomDep/sandbox.test.hs

+import Test.Cabal.Prelude
+main = cabalTest $ do
+    osx <- isOSX
+    -- On Travis OSX, Cabal shipped with GHC 7.8 does not work
+    -- with error "setup: /usr/bin/ar: permission denied"; see
+    -- also https://github.com/haskell/cabal/issues/3938
+    -- This is a hack to make the test not run in this case.
+    when osx $ skipUnless =<< ghcVersionIs (>= mkVersion [7,10])
+    withSandbox $ do
+        cabal_sandbox "add-source" ["custom"]
+        cabal_sandbox "add-source" ["client"]
+        -- NB: This test relies critically on the Setup script being
+        -- built against GHC's bundled Cabal.
+        cabal "install" ["client"]