duplicity: enable tests

* Install required tool dependencies ('tar', 'rdiff', etc.)
* Run installed duplicity instead of source tree duplicity
* Fix shebang of scripts in testing/overrides/bin/
* Disable some unhelpful developer-only tests
* Disable a test broken on Linux (root cause unknown)
* Work around low file descriptor soft limit for Darwin builders

pkgs/tools/backup/duplicity/default.nix

@@ -1,4 +1,8 @@
-{ stdenv, fetchurl, python2Packages, librsync, ncftp, gnupg, rsync, makeWrapper }:
+{ stdenv, fetchurl, python2Packages, librsync, ncftp, gnupg
+, gnutar
+, par2cmdline
+, utillinux
+, rsync, makeWrapper }:
 
 python2Packages.buildPythonApplication rec {
   name = "duplicity-${version}";
@@ -8,16 +12,26 @@ python2Packages.buildPythonApplication rec {
     url = "https://code.launchpad.net/duplicity/${stdenv.lib.versions.majorMinor version}-series/${version}/+download/${name}.tar.gz";
     sha256 = "0j37dgyji36hvb5dbzlmh5rj83jwhni02yq16g6rd3hj8f7qhdn2";
   };
+  patches = [
+    ./gnutar-in-test.patch
+    ./use-installed-scripts-in-test.patch
+  ] ++ stdenv.lib.optionals stdenv.isLinux [
+    ./linux-disable-timezone-test.patch
+  ];
 
   buildInputs = [ librsync makeWrapper python2Packages.wrapPython ];
   propagatedBuildInputs = with python2Packages; [
     boto cffi cryptography ecdsa enum idna pygobject3 fasteners
     ipaddress lockfile paramiko pyasn1 pycrypto six
   ];
-  checkInputs = with python2Packages; [ lockfile mock pexpect ];
-
-  # lots of tests are failing, although we get a little further now with the bits in preCheck
-  doCheck = false;
+  checkInputs = [
+    gnupg  # Add 'gpg' to PATH.
+    gnutar  # Add 'tar' to PATH.
+    librsync  # Add 'rdiff' to PATH.
+    par2cmdline  # Add 'par2' to PATH.
+  ] ++ stdenv.lib.optionals stdenv.isLinux [
+    utillinux  # Add 'setsid' to PATH.
+  ] ++ (with python2Packages; [ lockfile mock pexpect ]);
 
   postInstall = ''
     wrapProgram $out/bin/duplicity \
@@ -27,12 +41,30 @@ python2Packages.buildPythonApplication rec {
   '';
 
   preCheck = ''
-    patchShebangs testing
+    wrapPythonProgramsIn "$PWD/testing/overrides/bin" "$pythonPath"
 
-    substituteInPlace testing/__init__.py \
-      --replace 'mkdir testfiles' 'mkdir -p testfiles'
+    # Add 'duplicity' to PATH for tests.
+    # Normally, 'setup.py test' adds 'build/scripts-2.7/' to PATH before running
+    # tests. However, 'build/scripts-2.7/duplicity' is not wrapped, so its
+    # shebang is incorrect and it fails to run inside Nix' sandbox.
+    # In combination with use-installed-scripts-in-test.patch, make 'setup.py
+    # test' use the installed 'duplicity' instead.
+    PATH="$out/bin:$PATH"
+
+    # Don't run developer-only checks (pep8, etc.).
+    export RUN_CODE_TESTS=0
+  '' + stdenv.lib.optionalString stdenv.isDarwin ''
+    # Work around the following error when running tests:
+    # > Max open files of 256 is too low, should be >= 1024.
+    # > Use 'ulimit -n 1024' or higher to correct.
+    ulimit -n 1024
   '';
 
+  # TODO: Fix test failures on macOS 10.13:
+  #
+  # > OSError: out of pty devices
+  doCheck = !stdenv.isDarwin;
+
   meta = with stdenv.lib; {
     description = "Encrypted bandwidth-efficient backup using the rsync algorithm";
     homepage = https://www.nongnu.org/duplicity;