PosInformatique.UnitTests.Databases.SqlServer 1.0.1

PosInformatique.UnitTests.Databases

PosInformatique.UnitTests.Databases is a set of tools for unit testing databases. It simplifies writing and executing tests, helping ensure your database and data access code are reliable and bug-free. It is ideal for developers who want to validate data access based on SQL Server code during their development.

This set of tools supports unit testing of the data access layer based on SQL Server. Any kind of data access framework can be used with these tools:

• Raw ADO .NET queries.
• Entity Framework.
• Dapper.
• ...

The approach of these tools

The main approach of these tools is to perform unit tests without using mocking or in-memory alternatives for ADO .NET code or Entity Framework DbContext, instead using a real SQL Server database.

Why is this approach recommended?

• Around 30% to 40% of the code in applications is located in the Data Access layer or repository components. Because it is hard to unit test, developers often skip testing, resulting in lower code coverage.
• When using a mock or in-memory approach for a DbContext, you don't truly test the Entity Framework mapping to your database, especially additional SQL constraints like nullability, uniqueness, foreign key cascades, etc. You also miss technical behaviors like transactions, connection management, triggers, etc.
• When inserting data, it is crucial to ensure that the data in the columns are stored correctly (null/not null values, enum values to numerical values, custom or JSON serialized data, etc.).
• If you use Entity Framework, you can detect warnings/errors raised by the DbContext during the development.
• You perform unit test cases, meaning you write simple tests to validate small features instead of writing complex integration tests.

How to unit test a Data Access Layer

To perform unit tests of a Data Access Layer, the approach is straightforward using the Arrange/Act/Assert pattern:

Before each unit test (TestMethod or Fact methods):

1. Create an empty database with the SQL schema of the application.

   There are two ways to do this:

   • Deploy a DACPAC file (built by a SQL Server Database project).
   • Or create a database from a DbContext using Entity Framework.

2. Fill the tables with the sample data needed.

3. Execute the code (the method of the repository to be tested).

4. Assert the results of the executed code.

   • If the tested method returns data (performs a SELECT query), assert the returned objects using your favorite assertion framework (e.g., FluentAssertions).
   • If the method inserts, updates, or deletes data, assert the content of the tables to check that all data is stored correctly.

To write a unit test using this approach with the PosInformatique.UnitTests.Databases tools, see the Write unit tests to test the Data Access Layer page.

What do the PosInformatique.UnitTests.Databases tools provide?

Using the previous approach, the PosInformatique.UnitTests.Databases libraries allow you to:

• Easily deploy a database before each unit test execution. Database and schema creation can take a lot of time (around 5 to 10 seconds). The PosInformatique.UnitTests.Databases libraries physically create the database during the first unit test execution. For subsequent tests, all data is deleted in the database, which speeds up the unit test execution.

• Provide a simple syntax to fill the tables with sample data.

• Offer helpers to easily query and retrieve data from SQL tables (for assertions).

NuGet packages

The PosInformatique.UnitTests.Databases tools are provided in two NuGet packages:

• PosInformatique.UnitTests.Databases.SqlServer NuGet package which contains:

  • Tools to deploy a SQL Server database using a DACPAC file before each unit test.
  • Helpers to initialize SQL Server databases with sample data.
  • Helpers to easily query SQL Server databases.

• PosInformatique.UnitTests.Databases.SqlServer.EntityFramework NuGet package which contains:

  • Tools to deploy a SQL Server database using a DbContext.

  This package uses and includes the previous PosInformatique.UnitTests.Databases.SqlServer NuGet package.

Samples / Demo

A complete sample solution is available in this repository inside the samples folder.

The solution contains the following sample projects:

• DemoApp.Domain: Represents the domain of the application with a set of sample business entities.
• DemoApp.DataAccessLayer: Represents a Data Access Layer with a set of repositories to unit test.
• DemoApp.DataAccessLayer.Tests: Unit test project to test the DemoApp.DataAccessLayer project using the PosInformatique.UnitTests.Databases.SqlServer.EntityFramework package.

Writing unit tests for a Data Access Layer

To write unit tests for a Data Access Layer, follow the Write unit tests to test the Data Access Layer documentation page, which explains the different steps to perform using the PosInformatique.UnitTests.Databases.SqlServer.EntityFramework library:

• Create the SQL Server instance
  • Create the LocalDB instance
• Create the unit tests project
• Add the NuGet packages
• Unit test class
  • Deploy a new instance of the database from a DbContext
  • Parallel execution of the unit tests
  • Initialize the database data
• Write the unit tests for methods that retrieve data
• Write the unit tests for methods that update the data
• Execute the unit tests
• Check the database state after a unit test has failed