Add --https flag for e2e tests

This change introduces a --https flag similar to knative/serving#5157
to allow e2e tests to run correctly when the cluster is configured
with defaultExternalScheme=https.

Changes:
- Add test/e2e/e2e_flags.go with --https flag infrastructure
- Update domain_mapping_test.go to respect --https flag when determining expected URL schemes
- Update test/README.md with documentation for the new flag

The TestDomain test now adapts to cluster configuration:
- Without --https: Expects HTTP for regular services, HTTPS for TLS services
- With --https: Expects HTTPS for all services (matches defaultExternalScheme=https)

This fixes the issue where TestDomain fails when defaultExternalScheme is set to https.

Fixes: knative/serving#5157

Author: gouthamhusky

test/README.md

@@ -67,6 +67,18 @@ mode, use
 test/local-e2e-tests.sh -short
 ```
 
+### Running tests with HTTPS
+
+When running tests against a Knative cluster configured with `defaultExternalScheme=https`,
+use the `--https` flag to make tests expect HTTPS URLs for services:
+
+```bash
+test/local-e2e-tests.sh --https
+```
+
+This is particularly useful for the domain mapping tests, which need to know whether
+to expect HTTP or HTTPS URLs from services.
+
 ### Running E2E tests as a project admin
 
 It is possible to run the E2E tests by a user with reduced privileges, e.g. project admin.

test/e2e/domain_mapping_test.go

@@ -146,7 +146,8 @@ func domainDescribe(r *test.KnRunResultCollector, domainName string, tls bool) {
 	out := r.KnTest().Kn().Run("domain", "describe", domainName)
 	r.AssertNoError(out)
 	var url string
-	if tls {
+	// Use HTTPS if either TLS is explicitly configured or the --https flag is set
+	if tls || ClientFlags.HTTPS {
 		url = "https://" + domainName
 	} else {
 		url = "http://" + domainName

test/e2e/e2e_flags.go

@@ -0,0 +1,44 @@
+/*
+Copyright 2025 The Knative Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// This file contains logic to encapsulate flags which are needed to specify
+// what cluster, etc. to use for e2e tests.
+
+package e2e
+
+import (
+	"flag"
+
+	// Load the generic flags of knative.dev/pkg too.
+	_ "knative.dev/pkg/test"
+)
+
+// ClientFlags holds the flags or defaults for knative/client settings in the user's environment.
+var ClientFlags = initializeClientFlags()
+
+// ClientEnvironmentFlags holds the e2e flags needed only by the client repo.
+type ClientEnvironmentFlags struct {
+	HTTPS bool // Indicates where the test service will be created with https
+}
+
+func initializeClientFlags() *ClientEnvironmentFlags {
+	var f ClientEnvironmentFlags
+
+	flag.BoolVar(&f.HTTPS, "https", false,
+		"Set this flag to true to run all tests with https.")
+
+	return &f
+}