Fix max-num-spans flag's usage message (jaegertracing#2528)

Signed-off-by: albertteoh <albert.teoh@logz.io>

plugin/storage/es/options.go

@@ -179,9 +179,9 @@ func addFlags(flagSet *flag.FlagSet, nsConfig *namespaceConfig) {
 	flagSet.Int(
 		nsConfig.namespace+suffixMaxNumSpans,
 		nsConfig.MaxDocCount,
-		"(deprecated, will be removed in release v1.21.0. Please use es.max-doc-count). "+
+		"(deprecated, will be removed in release v1.21.0. Please use "+nsConfig.namespace+".max-doc-count). "+
 			"The maximum number of spans to fetch at a time per query in Elasticsearch. "+
-			"The lesser of es.max-num-spans and es.max-doc-count will be used if both are set.")
+			"The lesser of "+nsConfig.namespace+".max-num-spans and "+nsConfig.namespace+".max-doc-count will be used if both are set.")
 	flagSet.Int64(
 		nsConfig.namespace+suffixNumShards,
 		nsConfig.NumShards,

plugin/storage/es/options_test.go

@@ -96,6 +96,33 @@ func TestOptionsWithFlags(t *testing.T) {
 	assert.Equal(t, "test,tags", aux.Tags.Include)
 }
 
+func TestMaxNumSpansUsage(t *testing.T) {
+	testCases := []struct {
+		namespace string
+		wantUsage string
+	}{
+		{
+			namespace: "es",
+			wantUsage: "(deprecated, will be removed in release v1.21.0. Please use es.max-doc-count). " +
+				"The maximum number of spans to fetch at a time per query in Elasticsearch. " +
+				"The lesser of es.max-num-spans and es.max-doc-count will be used if both are set.",
+		},
+		{
+			namespace: "es-archive",
+			wantUsage: "(deprecated, will be removed in release v1.21.0. Please use es-archive.max-doc-count). " +
+				"The maximum number of spans to fetch at a time per query in Elasticsearch. " +
+				"The lesser of es-archive.max-num-spans and es-archive.max-doc-count will be used if both are set.",
+		},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.namespace, func(t *testing.T) {
+			opts := NewOptions(tc.namespace)
+			_, command := config.Viperize(opts.AddFlags)
+			assert.Equal(t, tc.wantUsage, command.Flag(tc.namespace+".max-num-spans").Usage)
+		})
+	}
+}
+
 func TestMaxDocCount(t *testing.T) {
 	testCases := []struct {
 		name            string