Seems to resolve the two tests that failed when run together as well as maintain the correct behavior of the issue-4637 example script

pipenv/core.py

@@ -1416,9 +1416,11 @@ def pip_install(
     if not index and requirement.index:
         index = requirement.index
     if index and not extra_indexes:
-        extra_indexes = list(project.sources)
+        extra_indexes = []
         if requirement.index:
-            extra_indexes = list(filter(lambda d: d['name'] == requirement.index, extra_indexes))
+            extra_indexes = list(filter(lambda d: d['name'] == requirement.index, project.sources))
+        if not extra_indexes:
+            extra_indexes = list(project.sources)
     if requirement and requirement.vcs or requirement.editable:
         requirement.index = None
         # Install dependencies when a package is a non-editable VCS dependency.

pipenv/utils.py

@@ -897,6 +897,7 @@ class Resolver:
         from pipenv.vendor.pip_shims.shims import InstallationError
         from pipenv.exceptions import ResolutionFailure
 
+        self.constraints  # For some reason its important to evaluate constraints before resolver context
         with temp_environ(), self.get_resolver() as resolver:
             try:
                 results = resolver.resolve(self.constraints, check_supported_wheels=False)