test: add tests and examples for ErrNotPermitted

Add TestErrNotPermitted to verify:
- ErrNotPermitted is distinct from ErrNotSupported
- Wrapped errors can be matched with errors.Is()

Update DocDetectXDP example to show how to handle
ErrNotPermitted in addition to ErrNotSupported.

Signed-off-by: Javier Cardona <jcardona@meta.com>

Author: javiercardona-work

docs/examples/features_test.go

@@ -16,13 +16,17 @@ func DocDetectXDP() {
 		fmt.Println("XDP program type is not supported")
 		return
 	}
+	if errors.Is(err, ebpf.ErrNotPermitted) {
+		fmt.Println("XDP program type is supported but permission denied")
+		return
+	}
 	if err != nil {
 		// Feature detection was inconclusive.
 		//
 		// Note: always log and investigate these errors! These can be caused
-		// by a lack of permissions, verifier errors, etc. Unless stated
-		// otherwise, probes are expected to be conclusive. Please file
-		// an issue if this is not the case in your environment.
+		// by verifier errors, etc. Unless stated otherwise, probes are
+		// expected to be conclusive. Please file an issue if this is not the
+		// case in your environment.
 		panic(err)
 	}
 

internal/feature_test.go

@@ -2,6 +2,7 @@ package internal
 
 import (
 	"errors"
+	"fmt"
 	"runtime"
 	"strings"
 	"testing"
@@ -88,3 +89,14 @@ func TestFeatureTestNotSupportedOnOS(t *testing.T) {
 		qt.Assert(t, qt.ErrorIs(NewFeatureTest("foo", fn, "1.0")(), sentinel))
 	}
 }
+
+func TestErrNotPermitted(t *testing.T) {
+	// ErrNotPermitted should be distinct from ErrNotSupported
+	qt.Assert(t, qt.Not(qt.ErrorIs(ErrNotPermitted, ErrNotSupported)))
+	qt.Assert(t, qt.Not(qt.ErrorIs(ErrNotSupported, ErrNotPermitted)))
+
+	// Wrapped errors should be matchable
+	wrapped := fmt.Errorf("%w: some details", ErrNotPermitted)
+	qt.Assert(t, qt.ErrorIs(wrapped, ErrNotPermitted))
+	qt.Assert(t, qt.Not(qt.ErrorIs(wrapped, ErrNotSupported)))
+}