build: finely sliced tox envs for testing pypy versions ad-hoc

Author: nedbat

tox.ini

@@ -24,7 +24,7 @@ install_command = python -m pip install -U {opts} {packages}
 
 passenv = *
 setenv =
-    pypy{3,37,38}: COVERAGE_NO_CTRACER=no C extension under PyPy
+    pypy{3,37,38,39}: COVERAGE_NO_CTRACER=no C extension under PyPy
     jython: COVERAGE_NO_CTRACER=no C extension under Jython
     jython: PYTEST_ADDOPTS=-n 0
     # For some tests, we need .pyc files written in the current directory,
@@ -51,6 +51,22 @@ commands =
 # For running against my own builds of CPython, or any other specific Python.
 basepython = {env:COVERAGE_ANYPY}
 
+[testenv:pypy37]
+basepython = pypy3.7
+
+[testenv:pypy38]
+basepython = pypy3.8
+
+[testenv:pypy37-rc]
+basepython = /usr/local/pypy/pypy3.7-v7.3.8rc1-osx64/bin/pypy3
+
+[testenv:pypy38-rc]
+basepython = /usr/local/pypy/pypy3.8-v7.3.8rc1-osx64/bin/pypy3
+
+[testenv:pypy39-rc]
+basepython = /usr/local/pypy/pypy3.9-v7.3.8rc1-osx64/bin/pypy3
+
+
 [testenv:doc]
 # Build the docs so we know if they are successful.  We build twice: once with
 # -q to get all warnings, and once with -QW to get a success/fail status