Add support for multiple output files in different formats (#732)

test/cli/trait_assertions_test.go

@@ -2,6 +2,7 @@ package cli
 
 import (
 	"encoding/json"
+	"os"
 	"regexp"
 	"strings"
 	"testing"
@@ -114,3 +115,12 @@ func assertSuccessfulReturnCode(tb testing.TB, _, _ string, rc int) {
 		tb.Errorf("expected no failure but got rc=%d", rc)
 	}
 }
+
+func assertFileExists(file string) traitAssertion {
+	return func(tb testing.TB, _, _ string, _ int) {
+		tb.Helper()
+		if _, err := os.Stat(file); err != nil {
+			tb.Errorf("expected file to exist %s", file)
+		}
+	}
+}