diff --git a/internal/testutil/fake_platform.go b/internal/testutil/fake_platform.go
new file mode 100644
index 0000000..c45f0ca
--- /dev/null
+++ b/internal/testutil/fake_platform.go
@@ -0,0 +1,40 @@
+// Package testutil provides test utilities for exercising the harness layer
+// against the OpenShell Go SDK fake, which validates the real sdkclient
+// mapping/translation without hitting a live gateway.
+package testutil
+
+import (
+	"context"
+
+	fake "github.com/NVIDIA/OpenShell/sdk/go/openshell/v1/fake"
+
+	"github.com/stackrox/harness-openshell/internal/openshell"
+	"github.com/stackrox/harness-openshell/internal/openshell/sdkclient"
+)
+
+// NewFake returns an openshell.Client backed by the SDK fake, exercising the
+// REAL sdkclient mapping/translation. Seed the fake via fake.With* options
+// before construction. For tests that need to call fake.Client.AddProvider
+// after construction, use NewFakeClient instead.
+func NewFake(workspace string, opts ...fake.ClientOption) openshell.Client {
+	c, _ := NewFakeClient(workspace, opts...)
+	return c
+}
+
+// NewFakeClient returns an openshell.Client backed by the SDK fake and the
+// underlying *fake.Client for direct test manipulation. This allows tests to
+// call fake.Client.AddProvider on the returned *fake.Client after construction.
+// Implement NewFake in terms of this to avoid duplication.
+func NewFakeClient(workspace string, opts ...fake.ClientOption) (openshell.Client, *fake.Client) {
+	raw := fake.NewClient(opts...)
+	return sdkclient.NewFromClient(raw, workspace), raw
+}
+
+// FakeFactory returns a Factory closure that ignores its context and Target
+// arguments and always returns the given Client and nil error. Use this to
+// wire a test client into code that depends on the Factory seam.
+func FakeFactory(c openshell.Client) openshell.Factory {
+	return func(context.Context, openshell.Target) (openshell.Client, error) {
+		return c, nil
+	}
+}
diff --git a/internal/testutil/fake_platform_test.go b/internal/testutil/fake_platform_test.go
new file mode 100644
index 0000000..fa8174c
--- /dev/null
+++ b/internal/testutil/fake_platform_test.go
@@ -0,0 +1,80 @@
+package testutil
+
+import (
+	"context"
+	"testing"
+
+	fake "github.com/NVIDIA/OpenShell/sdk/go/openshell/v1/fake"
+	"github.com/NVIDIA/OpenShell/sdk/go/openshell/v1/types"
+
+	"github.com/stackrox/harness-openshell/internal/openshell"
+)
+
+func TestHealthRoundTrip(t *testing.T) {
+	ctx := context.Background()
+	c := NewFake("default", fake.WithHealthResult(&types.HealthResult{
+		Healthy: true,
+		Version: "1.2.3",
+	}))
+
+	h, err := c.Health(ctx)
+	if err != nil {
+		t.Fatalf("Health() returned unexpected error: %v", err)
+	}
+	if !h.Healthy {
+		t.Errorf("expected Healthy=true, got %v", h.Healthy)
+	}
+	if h.Version != "1.2.3" {
+		t.Errorf("expected Version=%q, got %q", "1.2.3", h.Version)
+	}
+}
+
+func TestProvidersRoundTrip(t *testing.T) {
+	ctx := context.Background()
+	c, raw := NewFakeClient("default")
+	raw.AddProvider("default", &types.Provider{
+		Name: "p1",
+		Type: "openai",
+	})
+
+	providers, err := c.Providers(ctx)
+	if err != nil {
+		t.Fatalf("Providers() returned unexpected error: %v", err)
+	}
+	if len(providers) != 1 {
+		t.Fatalf("expected 1 provider, got %d", len(providers))
+	}
+	if providers[0].Name != "p1" {
+		t.Errorf("expected Name=%q, got %q", "p1", providers[0].Name)
+	}
+	if providers[0].Type != "openai" {
+		t.Errorf("expected Type=%q, got %q", "openai", providers[0].Type)
+	}
+}
+
+func TestEmptyProviders(t *testing.T) {
+	ctx := context.Background()
+	c := NewFake("default")
+
+	providers, err := c.Providers(ctx)
+	if err != nil {
+		t.Fatalf("Providers() returned unexpected error: %v", err)
+	}
+	if len(providers) != 0 {
+		t.Errorf("expected 0 providers, got %d", len(providers))
+	}
+}
+
+func TestFakeFactory(t *testing.T) {
+	ctx := context.Background()
+	c := NewFake("default")
+	f := FakeFactory(c)
+
+	got, err := f(ctx, openshell.Target{Gateway: "anything", Workspace: "x"})
+	if err != nil {
+		t.Errorf("FakeFactory returned unexpected error: %v", err)
+	}
+	if got != c {
+		t.Errorf("expected returned client to be the same as input")
+	}
+}