How to test database interactions in golang applications
Tags: go, testing, sql, webdev
Published: 2019-05-09 08:12:33

---
title: How to test database interactions in golang applications
published: true
description: Testing of functions with database interactions always was challenging. Recently, I found a wonderful library, which will simplify writing tests and mocking database queries in golang applications a lot. And I want to share a short example of how to work with it.
tags: go,testing,sql,webdev 
---

Testing of functions with database interactions always was challenging. Recently, I found a wonderful library [go-sqlmock](https://github.com/DATA-DOG/go-sqlmock) which will simplify writing tests and mocking database queries in golang applications a lot. And I want to share a short example of how to work with it.

First, we have to install it

`go get github.com/DATA-DOG/go-sqlmock`

 We have this function with SQL query:

```go
func MenuByNameAndLanguage(ctx context.Context, db *sql.DB, name string, langcode string) (*models.Menu, error) {
    result, err := db.Query("SELECT id, langcode, title, link__uri, view_sidemenu FROM menu_link_content_data WHERE menu_name=? AND langcode=?",
         name,
         langcode,
    )
    defer result.Close()
    
    var menuLinks []models.MenuLink
    for result.Next() {
         menuLink := models.MenuLink{}
         err = result.Scan(&menuLink.ID, &menuLink.Langcode, &menuLink.Title, &menuLink.URL, &menuLink.SideMenu)
         menuLinks = append(menuLinks, menuLink)    
    }
    menu := &models.Menu{
         Name: name,
         Links: menuLinks,
    }
    return menu, err
}
```
This function just getting menu links by menu name and language. 

And now let's test it.

We are going to test that MenuByNameAndLanguage function will return correct Menu structure.

```go
package menu


import (
    "context"
    "testing"


    "github.com/DATA-DOG/go-sqlmock"
    "github.com/stretchr/testify/assert"
    "gitlab.mfb.io/user/graphql_server/models"
)


func TestShouldReturnCorrectMenu(t *testing.T) {

    // Creates sqlmock database connection and a mock to manage expectations.
    db, mock, err := sqlmock.New()

    if err != nil {
        t.Fatalf("an error '%s' was not expected when opening a stub database connection", err)
    }
    // Closes the database and prevents new queries from starting.
    defer db.Close()

    // Here we are creating rows in our mocked database.
    rows := sqlmock.NewRows([]string{"id", "langcode", "title", "link__uri", "view_sidemenu"}).
        AddRow(1, "en", "enTitle", "/en-link", "0").
        AddRow(2, "en", "enTitle2", "/en-link2", "0")

    // This is most important part in our test. Here, literally, we are altering SQL query from MenuByNameAndLanguage
﻿    // function and replacing result with our expected result. 
    mock.ExpectQuery("^SELECT (.+) FROM menu_link_content_data*").
        WithArgs("main", "en").
        WillReturnRows(rows)


    ctx := context.TODO()

    // Calls MenuByNameAndLanguage with mocked database connection in arguments list. 
    menu, err := MenuByNameAndLanguage(ctx, db, "main", "en")

    // Here we just construction our expecting result.
    var menuLinks []models.MenuLink
    menuLink1 := models.MenuLink{
        ID:       1,
        Title:    "enTitle",
        Langcode: "en",
        URL:      "/en-link",
        SideMenu: "0",
    }
    menuLinks = append(menuLinks, menuLink1)

    menuLink2 := models.MenuLink{
        ID:       2,
        Title:    "enTitle2",
        Langcode: "en",
        URL:      "/en-link2",
        SideMenu: "0",
    }

    menuLinks = append(menuLinks, menuLink2)

    expectedMenu := &models.Menu{
        Name:  "main",
        Links: menuLinks,
    }
    
    // And, finally, let's check if result from MenuByNameAndLanguage equal with expected result.// Here I used Testify library (https://github.com/stretchr/testify).
    assert.Equal(t, expectedMenu, menu)
} 
```
As you see everything in this example was pretty straightforward.

For mo details, you can refer to [GoDocs](https://godoc.org/github.com/DATA-DOG/go-sqlmock).