refactor: add general-purpose test-mode signal in internal/test

Introduce test.IsTestMode(), backed by a compile-time const seeded by
two mutually-exclusive build-tagged files (test_mode_on.go under
-tags helmtest, test_mode_off.go otherwise). Branches gated on it
dead-code-eliminate in release builds.

Available for any production code path that needs to behave
differently under test. Not yet consumed — internal/version and
pkg/chart/common continue to gate on the KubeVersionMajorTesting /
KubeVersionMinorTesting sentinels seeded by
internal/version/version_helmtest.go.

Signed-off-by: Evans Mungai <mbuevans@gmail.com>

internal/test/test.go

@@ -27,6 +27,15 @@ import (
 // UpdateGolden writes out the golden files with the latest values, rather than failing the test.
 var updateGolden = flag.Bool("update", false, "update golden files")
 
+// IsTestMode reports whether the binary was built with -tags helmtest.
+// General-purpose signal that the binary was built for tests; consult it
+// from production code paths that need to behave differently under test.
+// Backed by a compile-time const (see test_mode_on.go / test_mode_off.go)
+// so branches gated on it dead-code-eliminate in release builds.
+func IsTestMode() bool {
+	return testMode
+}
+
 // TestingT describes a testing object compatible with the critical functions from the testing.T type
 type TestingT interface {
 	Fatal(...any)

internal/test/test_mode_off.go

@@ -0,0 +1,21 @@
+//go:build !helmtest
+
+/*
+Copyright The Helm 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.
+*/
+
+package test
+
+const testMode = false

internal/test/test_mode_on.go

@@ -0,0 +1,21 @@
+//go:build helmtest
+
+/*
+Copyright The Helm 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.
+*/
+
+package test
+
+const testMode = true