Initial tests for PEP 517 backend calls

tests/functional/test_pep517.py

@@ -0,0 +1,27 @@
+from pip._internal.build_env import BuildEnvironment
+from pip._internal.download import PipSession
+from pip._internal.index import PackageFinder
+from pip._internal.req import InstallRequirement
+
+from pip._vendor import pytoml
+
+
+def make_project(tmpdir, requires=[], backend=None):
+    buildsys = {'requires': requires}
+    if backend:
+        buildsys['build-backend'] = backend
+    data = pytoml.dumps({'build-system': buildsys})
+    tmpdir.join('pyproject.toml').write(data)
+    return tmpdir
+
+
+def test_backend(tmpdir, data):
+    """Can we call a requirement's backend successfully?"""
+    project = make_project(tmpdir, backend="dummy_backend")
+    req = InstallRequirement(None, None, source_dir=project)
+    env = BuildEnvironment()
+    finder = PackageFinder([data.backends], [], session=PipSession())
+    env.install_requirements(finder, ["dummy_backend"], "Installing")
+    assert hasattr(req.pep517_backend, 'build_wheel')
+    with env:
+        assert req.pep517_backend.build_wheel("dir") == "Backend called"

tests/lib/__init__.py

@@ -128,6 +128,10 @@ class TestData(object):
     def find_links3(self):
         return path_to_url(self.packages3)
 
+    @property
+    def backends(self):
+        return path_to_url(self.root.join("backends"))
+
     def index_url(self, index="simple"):
         return path_to_url(self.root.join("indexes", index))