Fix commit status index problem (#17061)

* Fix commit status index problem

* remove unused functions

* Add fixture and test for migration

* Fix lint

* Fix fixture

* Fix lint

* Fix test

* Fix bug

* Fix bug

models/migrations/v195_test.go

@@ -0,0 +1,62 @@
+// Copyright 2021 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 migrations
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_addTableCommitStatusIndex(t *testing.T) {
+	// Create the models used in the migration
+	type CommitStatus struct {
+		ID     int64  `xorm:"pk autoincr"`
+		Index  int64  `xorm:"INDEX UNIQUE(repo_sha_index)"`
+		RepoID int64  `xorm:"INDEX UNIQUE(repo_sha_index)"`
+		SHA    string `xorm:"VARCHAR(64) NOT NULL INDEX UNIQUE(repo_sha_index)"`
+	}
+
+	// Prepare and load the testing database
+	x, deferable := prepareTestEnv(t, 0, new(CommitStatus))
+	if x == nil || t.Failed() {
+		defer deferable()
+		return
+	}
+	defer deferable()
+
+	// Run the migration
+	if err := addTableCommitStatusIndex(x); err != nil {
+		assert.NoError(t, err)
+		return
+	}
+
+	type CommitStatusIndex struct {
+		ID       int64
+		RepoID   int64  `xorm:"unique(repo_sha)"`
+		SHA      string `xorm:"unique(repo_sha)"`
+		MaxIndex int64  `xorm:"index"`
+	}
+
+	var start = 0
+	const batchSize = 1000
+	for {
+		var indexes = make([]CommitStatusIndex, 0, batchSize)
+		err := x.Table("commit_status_index").Limit(batchSize, start).Find(&indexes)
+		assert.NoError(t, err)
+
+		for _, idx := range indexes {
+			var maxIndex int
+			has, err := x.SQL("SELECT max(`index`) FROM commit_status WHERE repo_id = ? AND sha = ?", idx.RepoID, idx.SHA).Get(&maxIndex)
+			assert.NoError(t, err)
+			assert.True(t, has)
+			assert.EqualValues(t, maxIndex, idx.MaxIndex)
+		}
+		if len(indexes) < batchSize {
+			break
+		}
+		start += len(indexes)
+	}
+}