diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 7aa19972f..ed5c2929c 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -232,6 +232,22 @@ guide](https://helm.sh/docs/community/developers/) to get started.
 Coding conventions and standards are explained in the [official developer
 docs](https://helm.sh/docs/developers/).
 
+### Running tests
+
+Use the Makefile targets (`make test`, `make test-unit`, `make test-coverage`)
+rather than invoking `go test ./...` directly. The Makefile passes the
+`helmtest` build tag, which is required: it selects
+`internal/testmode/mode_on.go` (setting `const testMode = true`), enabling
+`testmode.IsTestMode()` so production code paths in `internal/version` and
+`pkg/chart/common` substitute stable values instead of reading build info.
+Test binaries have no module info, so without this tag those code paths
+panic during package init.
+
+If you run tests outside the Makefile (IDE test runners, `go test` directly,
+custom CI), pass `-tags helmtest`. The tag is omitted from release builds so
+the `testing` package and its dependencies stay out of shipped binaries, and
+branches gated on `testmode.IsTestMode()` are dead-code-eliminated by the compiler.
+
 ## Pull Requests
 
 Like any good open source project, we use Pull Requests (PRs) to track code changes.
diff --git a/Makefile b/Makefile
index 81b149a68..bf78d5511 100644
--- a/Makefile
+++ b/Makefile
@@ -90,6 +90,13 @@ test: test-style
 test: test-unit
 
 .PHONY: test-unit
+# The `helmtest` build tag selects internal/testmode/mode_on.go, flipping
+# testmode.IsTestMode() to true so production code paths in internal/version
+# and pkg/chart/common substitute stable values instead of reading missing
+# module info. Attached to test-unit (not the file-level TESTFLAGS) so the
+# tag is guaranteed regardless of any target-specific TESTFLAGS overrides
+# in upstream targets (e.g. gen-test-golden).
+test-unit: TESTFLAGS += -tags helmtest
 test-unit:
 	@echo
 	@echo "==> Running unit tests <=="
@@ -150,7 +157,7 @@ format: $(GOIMPORTS)
 .PHONY: gen-test-golden
 gen-test-golden:
 gen-test-golden: PKG = ./pkg/cmd ./pkg/action
-gen-test-golden: TESTFLAGS = -update
+gen-test-golden: TESTFLAGS += -update
 gen-test-golden: test-unit
 
 # ------------------------------------------------------------------------------
diff --git a/internal/testmode/mode_off.go b/internal/testmode/mode_off.go
new file mode 100644
index 000000000..ea3e52560
--- /dev/null
+++ b/internal/testmode/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 testmode
+
+const testMode = false
diff --git a/internal/testmode/mode_on.go b/internal/testmode/mode_on.go
new file mode 100644
index 000000000..045d6e2c1
--- /dev/null
+++ b/internal/testmode/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 testmode
+
+const testMode = true
diff --git a/internal/testmode/testmode.go b/internal/testmode/testmode.go
new file mode 100644
index 000000000..a2be02709
--- /dev/null
+++ b/internal/testmode/testmode.go
@@ -0,0 +1,31 @@
+/*
+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 testmode exposes a compile-time test-mode signal that production
+// code paths may consult when they need to behave differently in a `go
+// test` binary. The package has no imports and no init side effects, so it
+// can be safely linked from release builds: branches gated on IsTestMode()
+// are dead-code-eliminated by the compiler.
+package testmode
+
+// 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 mode_on.go / mode_off.go) so branches
+// gated on it dead-code-eliminate in release builds.
+func IsTestMode() bool {
+	return testMode
+}
diff --git a/internal/version/version.go b/internal/version/version.go
index 572938c96..165d4f22c 100644
--- a/internal/version/version.go
+++ b/internal/version/version.go
@@ -17,14 +17,14 @@ limitations under the License.
 package version
 
 import (
-	"flag"
 	"fmt"
 	"log/slog"
 	"runtime"
 	"strings"
-	"testing"
 
 	"github.com/Masterminds/semver/v3"
+
+	"helm.sh/helm/v4/internal/testmode"
 )
 
 var (
@@ -44,8 +44,14 @@ var (
 	gitTreeState = ""
 )
 
+// Stub Kubernetes version values for use by any test path that needs a
+// stable kube major/minor — for example, substituting into capabilities or
+// client-go version strings so test output doesn't drift with the
+// k8s.io/client-go version pinned in go.mod. Callers decide when to use
+// them; they are not tied to any particular build tag or gating mechanism.
 const (
-	kubeClientGoVersionTesting = "v1.20"
+	KubeVersionMajorTesting uint64 = 1
+	KubeVersionMinorTesting uint64 = 20
 )
 
 // BuildInfo describes the compile time information.
@@ -81,8 +87,8 @@ func Get() BuildInfo {
 		// Test builds don't include debug info / module info
 		// (And even if they did, we probably want a stable version during tests anyway)
 		// Return a default value for test builds
-		if testing.Testing() {
-			return kubeClientGoVersionTesting
+		if testmode.IsTestMode() {
+			return fmt.Sprintf("v%d.%d", KubeVersionMajorTesting, KubeVersionMinorTesting)
 		}
 
 		vstr, err := K8sIOClientGoModVersion()
@@ -112,7 +118,7 @@ func Get() BuildInfo {
 	}
 
 	// HACK(bacongobbler): strip out GoVersion during a test run for consistent test output
-	if flag.Lookup("test.v") != nil {
+	if testmode.IsTestMode() {
 		v.GoVersion = ""
 	}
 	return v
diff --git a/pkg/chart/common/capabilities.go b/pkg/chart/common/capabilities.go
index 16910acaa..1b165c281 100644
--- a/pkg/chart/common/capabilities.go
+++ b/pkg/chart/common/capabilities.go
@@ -20,7 +20,6 @@ import (
 	"slices"
 	"strconv"
 	"strings"
-	"testing"
 
 	"github.com/Masterminds/semver/v3"
 	"k8s.io/client-go/kubernetes/scheme"
@@ -29,14 +28,10 @@ import (
 	apiextensionsv1beta1 "k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1beta1"
 	k8sversion "k8s.io/apimachinery/pkg/util/version"
 
+	"helm.sh/helm/v4/internal/testmode"
 	helmversion "helm.sh/helm/v4/internal/version"
 )
 
-const (
-	kubeVersionMajorTesting = 1
-	kubeVersionMinorTesting = 20
-)
-
 var (
 	// DefaultVersionSet is the default version set, which includes only Core V1 ("v1").
 	DefaultVersionSet = allKnownVersions()
@@ -146,8 +141,8 @@ func makeDefaultCapabilities() (*Capabilities, error) {
 	// Test builds don't include debug info / module info
 	// (And even if they did, we probably want stable capabilities for tests anyway)
 	// Return a default value for test builds
-	if testing.Testing() {
-		return newCapabilities(kubeVersionMajorTesting, kubeVersionMinorTesting)
+	if testmode.IsTestMode() {
+		return newCapabilities(helmversion.KubeVersionMajorTesting, helmversion.KubeVersionMinorTesting)
 	}
 
 	vstr, err := helmversion.K8sIOClientGoModVersion()
diff --git a/scripts/coverage.sh b/scripts/coverage.sh
index 4a29a68ad..b07d5d7fd 100755
--- a/scripts/coverage.sh
+++ b/scripts/coverage.sh
@@ -37,7 +37,7 @@ generate_cover_data() {
   for d in $(go list "$target"); do
     (
       local output="${coverdir}/${d//\//-}.cover"
-      go test -coverprofile="${output}" -covermode="$covermode" "$d"
+      go test -tags helmtest -coverprofile="${output}" -covermode="$covermode" "$d"
     )
   done