chore: testing constraints target minimum supported versions

gapic/templates/setup.py.j2

@@ -33,7 +33,7 @@ else:
     release_status = "Development Status :: 5 - Production/Stable"
 
 dependencies = [
-    "google-api-core[grpc] >= 2.11.0, <3.0.0",
+    "google-api-core[grpc] >= 2.21.0, <3.0.0",
     # Exclude incompatible versions of `google-auth`
     # See https://github.com/googleapis/google-cloud-python/issues/12364
     "google-auth >= 2.14.1, <3.0.0,!=2.24.0,!=2.25.0",

gapic/templates/testing/constraints-3.9.txt.j2

@@ -7,7 +7,7 @@
 # For example, if setup.py has "google-cloud-foo >= 1.14.0, < 2.0.0",
 # then this file should have google-cloud-foo==1.14.0
 google-api-core==2.21.0
-google-auth==2.35.0
+google-auth==2.14.1
 # TODO(https://github.com/googleapis/gapic-generator-python/issues/2453)
 # Add the minimum supported version of grpcio to constraints files
 proto-plus==1.22.3

noxfile.py

@@ -357,13 +357,20 @@ def showcase_library(
             constraints_path = str(
                 f"{tmp_dir}/testing/constraints-{session.python}.txt"
             )
-            # Install the library with a constraints file.
-            session.install(
-                "-e",
-                tmp_dir + ("[async_rest]" if rest_async_io_enabled else ""),
-                "-r",
-                constraints_path,
-            )
+            if not rest_async_io_enabled:
+                # Install the library with a constraints file.
+                session.install("-e", tmp_dir, "-r", constraints_path)
+            else:
+                # modify constraints file to support async_rest
+                constraints = [
+                    line.strip()
+                    for line in open(constraints_path)
+                    if "google-auth" not in line
+                    and not line.startswith("#")
+                    and line.strip()
+                ]
+                session.install("-e", f"{tmp_dir}[async_rest]", *constraints)
+
             # Exclude `google-auth==2.40.0` which contains a regression
             # https://github.com/googleapis/gapic-generator-python/issues/2385
             session.install(