Demonstrates a Possible Issue with the Flask Test Client

issue.py

from flask import Flask, Blueprint
app = Flask(__name__)

bp = Blueprint("test", __name__)
@bp.route("/test/")
def test():
    return "TEST"
    
app.register_blueprint(bp, subdomain="test")

app.config["PREFERRRED_URL_SCHEME"] = "http"
app.config["SERVER_NAME"] = "domain.tld:80"

with app.test_client() as c:
    c.get("/test/", base_url="http://test.domain.tld:80") # Will return 404
    c.get("/test/", base_url="http://test.domain.tld") # Will return 404
    
app.config["SERVER_NAME"] = "domain.tld"
with app.test_client() as c:
    c.get("/test/", base_url="http://test.domain.tld:80") # Will return 200
    c.get("/test/", base_url="http://test.domain.tld") # Will return 200
    
app.config["SERVER_NAME"] = "domain.tld:5000"
with app.test_client() as c:
    c.get("/test/", base_url="http://test.domain.tld:5000") # Will return 200
    c.get("/test/", base_url="http://test.domain.tld") # Will return 404