chore: installation of test packages in eachdist (#794)

eachdist.py did not support the installation of test packages,
(as defined by the extra_requires:test package group). As a
result, test packages were being added to dev-requirements.txt

By having eachdist.py develop install test packages, and moving
develop/test package definitions to the individual instrumentations,
it is easier to determine which packages require which dependencies
for testing purposes, and enables support for existing dependencies
that follow the extra_requires:test pattern.

scripts/eachdist.py

@@ -205,6 +205,7 @@ def parse_args(args=None):
 
     setup_instparser(instparser)
     instparser.add_argument("--editable", "-e", action="store_true")
+    instparser.add_argument("--with-test-deps", action="store_true")
     instparser.add_argument("--with-dev-deps", action="store_true")
     instparser.add_argument("--eager-upgrades", action="store_true")
 
@@ -214,7 +215,10 @@ def parse_args(args=None):
     )
     setup_instparser(devparser)
     devparser.set_defaults(
-        editable=True, with_dev_deps=True, eager_upgrades=True
+        editable=True,
+        with_dev_deps=True,
+        eager_upgrades=True,
+        with_test_deps=True,
     )
 
     lintparser = subparsers.add_parser(
@@ -424,7 +428,16 @@ def install_args(args):
             check=True,
         )
 
-    allfmt = "-e 'file://{}'" if args.editable else "'file://{}'"
+    allfmt = "-e 'file://{}" if args.editable else "'file://{}"
+    # packages should provide an extra_requires that is named
+    # 'test', to denote test dependencies.
+    extras = []
+    if args.with_test_deps:
+        extras.append("test")
+    if extras:
+        allfmt += "[{}]".format(",".join(extras))
+    # note the trailing single quote, to close the quote opened above.
+    allfmt += "'"
     execute_args(
         parse_subargs(
             args,