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/v176_test.go

@@ -0,0 +1,128 @@
+// 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_removeInvalidLabels(t *testing.T) {
+	// Models used by the migration
+	type Comment struct {
+		ID           int64 `xorm:"pk autoincr"`
+		Type         int   `xorm:"INDEX"`
+		IssueID      int64 `xorm:"INDEX"`
+		LabelID      int64
+		ShouldRemain bool // <- Flag for testing the migration
+	}
+
+	type Issue struct {
+		ID     int64 `xorm:"pk autoincr"`
+		RepoID int64 `xorm:"INDEX UNIQUE(repo_index)"`
+		Index  int64 `xorm:"UNIQUE(repo_index)"` // Index in one repository.
+	}
+
+	type Repository struct {
+		ID        int64  `xorm:"pk autoincr"`
+		OwnerID   int64  `xorm:"UNIQUE(s) index"`
+		LowerName string `xorm:"UNIQUE(s) INDEX NOT NULL"`
+	}
+
+	type Label struct {
+		ID     int64 `xorm:"pk autoincr"`
+		RepoID int64 `xorm:"INDEX"`
+		OrgID  int64 `xorm:"INDEX"`
+	}
+
+	type IssueLabel struct {
+		ID           int64 `xorm:"pk autoincr"`
+		IssueID      int64 `xorm:"UNIQUE(s)"`
+		LabelID      int64 `xorm:"UNIQUE(s)"`
+		ShouldRemain bool  // <- Flag for testing the migration
+	}
+
+	// load and prepare the test database
+	x, deferable := prepareTestEnv(t, 0, new(Comment), new(Issue), new(Repository), new(IssueLabel), new(Label))
+	if x == nil || t.Failed() {
+		defer deferable()
+		return
+	}
+	defer deferable()
+
+	var issueLabels []*IssueLabel
+	ilPreMigration := map[int64]*IssueLabel{}
+	ilPostMigration := map[int64]*IssueLabel{}
+
+	var comments []*Comment
+	comPreMigration := map[int64]*Comment{}
+	comPostMigration := map[int64]*Comment{}
+
+	// Get pre migration values
+	if err := x.Find(&issueLabels); err != nil {
+		t.Errorf("Unable to find issueLabels: %v", err)
+		return
+	}
+	for _, issueLabel := range issueLabels {
+		ilPreMigration[issueLabel.ID] = issueLabel
+	}
+	if err := x.Find(&comments); err != nil {
+		t.Errorf("Unable to find comments: %v", err)
+		return
+	}
+	for _, comment := range comments {
+		comPreMigration[comment.ID] = comment
+	}
+
+	// Run the migration
+	if err := removeInvalidLabels(x); err != nil {
+		t.Errorf("unable to RemoveInvalidLabels: %v", err)
+	}
+
+	// Get the post migration values
+	issueLabels = issueLabels[:0]
+	if err := x.Find(&issueLabels); err != nil {
+		t.Errorf("Unable to find issueLabels: %v", err)
+		return
+	}
+	for _, issueLabel := range issueLabels {
+		ilPostMigration[issueLabel.ID] = issueLabel
+	}
+	comments = comments[:0]
+	if err := x.Find(&comments); err != nil {
+		t.Errorf("Unable to find comments: %v", err)
+		return
+	}
+	for _, comment := range comments {
+		comPostMigration[comment.ID] = comment
+	}
+
+	// Finally test results of the migration
+	for id, comment := range comPreMigration {
+		post, ok := comPostMigration[id]
+		if ok {
+			if !comment.ShouldRemain {
+				t.Errorf("Comment[%d] remained but should have been deleted", id)
+			}
+			assert.Equal(t, comment, post)
+		} else if comment.ShouldRemain {
+			t.Errorf("Comment[%d] was deleted but should have remained", id)
+		}
+	}
+
+	for id, il := range ilPreMigration {
+		post, ok := ilPostMigration[id]
+		if ok {
+			if !il.ShouldRemain {
+				t.Errorf("IssueLabel[%d] remained but should have been deleted", id)
+			}
+			assert.Equal(t, il, post)
+		} else if il.ShouldRemain {
+			t.Errorf("IssueLabel[%d] was deleted but should have remained", id)
+		}
+	}
+
+}