prevent empty review comment (#4632)

* prevent empty review comment

This would only require a comment for rejection and comment

* add tests

* add comment

modules/auth/repo_form_test.go

@@ -0,0 +1,41 @@
+// Copyright 2018 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package auth
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSubmitReviewForm_IsEmpty(t *testing.T) {
+
+	cases := []struct {
+		form     SubmitReviewForm
+		expected bool
+	}{
+		// Approved PR with a comment shouldn't count as empty
+		{SubmitReviewForm{Type: "approve", Content: "Awesome"}, false},
+
+		// Approved PR without a comment shouldn't count as empty
+		{SubmitReviewForm{Type: "approve", Content: ""}, false},
+
+		// Rejected PR without a comment should count as empty
+		{SubmitReviewForm{Type: "reject", Content: ""}, true},
+
+		// Rejected PR with a comment shouldn't count as empty
+		{SubmitReviewForm{Type: "reject", Content: "Awesome"}, false},
+
+		// Comment review on a PR with a comment shouldn't count as empty
+		{SubmitReviewForm{Type: "comment", Content: "Awesome"}, false},
+
+		// Comment review on a PR without a comment should count as empty
+		{SubmitReviewForm{Type: "comment", Content: ""}, true},
+	}
+
+	for _, v := range cases {
+		assert.Equal(t, v.expected, v.form.HasEmptyContent())
+	}
+}