etw: Add test for provider name to GUID conversion

Also simplified the name to GUID conversion code, and improved the
comments.

Signed-off-by: Kevin Parsons <kevpar@microsoft.com>

pkg/etw/provider_test.go

@@ -0,0 +1,34 @@
+package etw
+
+import (
+	"testing"
+
+	"github.com/Microsoft/go-winio/pkg/guid"
+)
+
+func mustGUIDFromString(t *testing.T, s string) guid.GUID {
+	g, err := guid.FromString(s)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return g
+}
+
+func Test_ProviderIDFromName(t *testing.T) {
+	type testCase struct {
+		name string
+		g    guid.GUID
+	}
+	testCases := []testCase{
+		{"wincni", mustGUIDFromString(t, "c822b598-f4cc-5a72-7933-ce2a816d033f")},
+		{"Moby", mustGUIDFromString(t, "6996f090-c5de-5082-a81e-5841acc3a635")},
+		{"ContainerD", mustGUIDFromString(t, "2acb92c0-eb9b-571a-69cf-8f3410f383ad")},
+		{"Microsoft.Virtualization.RunHCS", mustGUIDFromString(t, "0B52781F-B24D-5685-DDF6-69830ED40EC3")},
+	}
+	for _, tc := range testCases {
+		g := providerIDFromName(tc.name)
+		if g != tc.g {
+			t.Fatalf("Incorrect provider GUID.\nExpected: %s\nActual: %s", tc.g, g)
+		}
+	}
+}