Add IsEnclave to facilitate testing.

This allows unit tests to skip a test if we're not running inside an
enclave.

internal/enclave/pcr_test.go

@@ -8,9 +8,17 @@ import (
 )
 
 func TestGetPCRs(t *testing.T) {
-	_, err := getPCRs()
-	// We expect an error when asking for PCRs outside of an enclave.
-	require.Error(t, err)
+	if !IsEnclave() {
+		t.Skip("skipping test; not running in an enclave")
+	}
+
+	pcrs1, err := getPCRs()
+	require.NoError(t, err)
+
+	pcrs2, err := getPCRs()
+	require.NoError(t, err)
+
+	assert.False(t, pcrs1.Equal(pcrs2))
 }
 
 func TestPCRsEqual(t *testing.T) {

internal/enclave/util.go

@@ -0,0 +1,11 @@
+package enclave
+
+// IsEnclave returns true if the current process is running in an enclave.
+func IsEnclave() bool {
+	// The most straightforward way to determine if we're running in an enclave
+	// is to try and request an attestation document.
+	if _, err := getPCRs(); err == nil {
+		return true
+	}
+	return false
+}