Added EXPLAIN_TEMPLATE_LOADING to help people debug templates not being loaded.

flask/testsuite/test_apps/blueprintapp/__init__.py

@@ -1,6 +1,7 @@
 from flask import Flask
 
 app = Flask(__name__)
+app.config['DEBUG'] = True
 from blueprintapp.apps.admin import admin
 from blueprintapp.apps.frontend import frontend
 app.register_blueprint(admin)

flask/testsuite/test_apps/blueprintapp/apps/frontend/__init__.py

@@ -6,3 +6,8 @@ frontend = Blueprint('frontend', __name__, template_folder='templates')
 @frontend.route('/')
 def index():
     return render_template('frontend/index.html')
+
+
+@frontend.route('/missing')
+def missing_template():
+    return render_template('missing_template.html')