Create Proper Migration Tests (#15116)

* Create Proper Migration tests

Unfortunately our testing regime has so far meant that migrations do not
get proper testing.

This PR begins the process of creating migration tests for this.

* Add test for v176

* fix mssql drop db

Signed-off-by: Andrew Thornton <art27@cantab.net>

models/migrations/v177_test.go

@@ -0,0 +1,88 @@
+// 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"
+
+	"code.gitea.io/gitea/modules/timeutil"
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_deleteOrphanedIssueLabels(t *testing.T) {
+	// Create the models used in the migration
+	type IssueLabel struct {
+		ID      int64 `xorm:"pk autoincr"`
+		IssueID int64 `xorm:"UNIQUE(s)"`
+		LabelID int64 `xorm:"UNIQUE(s)"`
+	}
+
+	type Label struct {
+		ID              int64 `xorm:"pk autoincr"`
+		RepoID          int64 `xorm:"INDEX"`
+		OrgID           int64 `xorm:"INDEX"`
+		Name            string
+		Description     string
+		Color           string `xorm:"VARCHAR(7)"`
+		NumIssues       int
+		NumClosedIssues int
+		CreatedUnix     timeutil.TimeStamp `xorm:"INDEX created"`
+		UpdatedUnix     timeutil.TimeStamp `xorm:"INDEX updated"`
+	}
+
+	// Prepare and load the testing database
+	x, deferable := prepareTestEnv(t, 0, new(IssueLabel), new(Label))
+	if x == nil || t.Failed() {
+		defer deferable()
+		return
+	}
+	defer deferable()
+
+	var issueLabels []*IssueLabel
+	preMigration := map[int64]*IssueLabel{}
+	postMigration := map[int64]*IssueLabel{}
+
+	// Load issue labels that exist in the database pre-migration
+	if err := x.Find(&issueLabels); err != nil {
+		assert.NoError(t, err)
+		return
+	}
+	for _, issueLabel := range issueLabels {
+		preMigration[issueLabel.ID] = issueLabel
+	}
+
+	// Run the migration
+	if err := deleteOrphanedIssueLabels(x); err != nil {
+		assert.NoError(t, err)
+		return
+	}
+
+	// Load the remaining issue-labels
+	issueLabels = issueLabels[:0]
+	if err := x.Find(&issueLabels); err != nil {
+		assert.NoError(t, err)
+		return
+	}
+	for _, issueLabel := range issueLabels {
+		postMigration[issueLabel.ID] = issueLabel
+	}
+
+	// Now test what is left
+	if _, ok := postMigration[2]; ok {
+		t.Errorf("Orphaned Label[2] survived the migration")
+		return
+	}
+
+	if _, ok := postMigration[5]; ok {
+		t.Errorf("Orphaned Label[5] survived the migration")
+		return
+	}
+
+	for id, post := range postMigration {
+		pre := preMigration[id]
+		assert.Equal(t, pre, post, "migration changed issueLabel %d", id)
+	}
+
+}