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Write tests with Testcontainers

Table of contents

Add Testcontainers dependencies

Add the Testcontainers PostgreSQL module to the test project:

$ dotnet add ./CustomerService.Tests/CustomerService.Tests.csproj package Testcontainers.PostgreSql

Write the test

Create CustomerServiceTest.cs in the test project:

using Testcontainers.PostgreSql;

namespace Customers.Tests;

public sealed class CustomerServiceTest : IAsyncLifetime
{
    private readonly PostgreSqlContainer _postgres = new PostgreSqlBuilder()
        .WithImage("postgres:16-alpine")
        .Build();

    public Task InitializeAsync()
    {
        return _postgres.StartAsync();
    }

    public Task DisposeAsync()
    {
        return _postgres.DisposeAsync().AsTask();
    }

    [Fact]
    public void ShouldReturnTwoCustomers()
    {
        // Given
        var customerService = new CustomerService(new DbConnectionProvider(_postgres.GetConnectionString()));

        // When
        customerService.Create(new Customer(1, "George"));
        customerService.Create(new Customer(2, "John"));
        var customers = customerService.GetCustomers();

        // Then
        Assert.Equal(2, customers.Count());
    }
}

Here's what the test does:

  • Declares a PostgreSqlContainer using the PostgreSqlBuilder with the postgres:16-alpine Docker image.
  • Implements IAsyncLifetime for container lifecycle management:
    • InitializeAsync() starts the container before the test runs.
    • DisposeAsync() stops and removes the container after the test finishes.
  • ShouldReturnTwoCustomers() creates a CustomerService with connection details from the container, inserts two customers, fetches all customers, and asserts the count.
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