tests: verify to handle dependencies conditional on other dependencies

var/spack/repos/builtin.mock/packages/py-extension3/package.py

@@ -0,0 +1,21 @@
+# Copyright 2013-2020 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+class PyExtension3(Package):
+    """Package with a dependency whose presence is conditional to the
+    version of Python being used.
+    """
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/extension3-1.0.tar.gz"
+
+    depends_on("python")
+    depends_on('py-extension1', type=('build', 'run'), when='^python@:2.8.0')
+
+    depends_on('patchelf@0.9', when='@1.0:1.1 ^python@:2')
+    depends_on('patchelf@0.10', when='@1.0:1.1 ^python@3:')
+
+    version('2.0', 'hash-extension3-1.0')
+    version('1.1', 'hash-extension3-1.0')
+    version('1.0', 'hash-extension3-1.0')