use pyproject.toml to specify build dependencies

.travis.yml

@@ -34,7 +34,7 @@ install:  # Install our test dependencies.
 
 script:  # Run our test suite.
   - if [[ -n $COVERAGE ]]; then export PYTEST_ADDOPTS="--cov=bidict --cov-config=.coveragerc"; fi
-  - python setup.py test
+  - pytest tests
 
 
 after_script:

pyproject.toml

@@ -0,0 +1,7 @@
+[build-system]
+requires = [
+    "setuptools >= 35.0.2",
+    "wheel >= 0.29.0",
+    "setuptools_scm"
+]
+build-backend = 'setuptools.build_meta'

setup.py

@@ -40,12 +40,7 @@ else:
 with c_open(join(CWD, 'README.rst'), encoding='utf-8') as f:
     LONG_DESCRIPTION = f.read()
 
-
-SETUP_REQS = [
-    'pytest-runner',
-    'setuptools_scm',
-]
-
+SETUP_REQS = ['setuptools_scm']
 TEST_REQS = [
     'hypothesis<4',
     'hypothesis-pytest<1',
@@ -108,7 +103,8 @@ setup(
         'Programming Language :: Python :: Implementation :: PyPy',
         'Topic :: Software Development :: Libraries :: Python Modules',
     ],
-    setup_requires=SETUP_REQS,
+    setup_requires=SETUP_REQS,  # required so pip < 10 install works (no PEP-517/8 support)
+    # for more details see https://www.python.org/dev/peps/pep-0518/#rationale
     tests_require=TEST_REQS,
     extras_require=dict(
         test=TEST_REQS,