Presentation integration tests (Lambda function)

The rule

tests/Presentation.Tests.Integration tests the whole function in memory by calling Handler methods the way Lambda does. Each test class creates one Handler from the services Startup registers, with its own shared-cache in-memory SQLite database and the sample data on, and a TestLambdaContext (from Amazon.Lambda.TestUtilities) with time remaining.

The serializer is tested on its own in tests/Presentation.Tests.Unit (unit-tests, json-serialization).

There are two ways in, and tests use whichever the case needs:

Steps

1. Use the class's handler and context fields. Create a second handler with CreateHandler only when the test needs other settings.
2. Call the function, then assert the result: counts, NextOffset, and that every item matches the filter.
3. Failures: await Should.ThrowAsync<ValidationException>(...) and check the property name in the errors, or NotFoundException and its message.
4. Find the rows you need through another function (list, then pick one), not by hard-coded ids. Sample data ids are random.
5. For an Http* function, turn the IHttpResult into the API Gateway response with Read, then read the body with Body<T>. Check the content type with ContentType, which reads the raw JSON: Lambda Annotations writes header names in lower case and the SDK's response type doesn't read them back.
6. A test that sets environment variables clears them in finally.
7. Write one test per success and per failure the function can return (test-design).

Example

// tests/Presentation.Tests.Integration/HandlerTests.cs
private readonly Handler handler = CreateHandler(new()
{
    ["ConnectionStrings:MovieReviews"] = InMemoryDatabase(),
    ["Database:SeedSampleData"] = "true"
});
private readonly TestLambdaContext context = new() { RemainingTime = TimeSpan.FromSeconds(30) };

[Fact]
public async Task GetMovies_ShouldThrow_WhenLimitIsNotValid()
{
    // Act
    var exception = await Should.ThrowAsync<ValidationException>(() => this.handler.GetMovies(new ListRequest { Limit = 0 }, this.context));

    // Assert
    exception.Errors.ShouldContain(e => e.PropertyName == "Limit" && e.ErrorMessage == "A limit must be between 1 and 50.");
}

Don't

• Share a Handler across test classes or in a static field. Each class gets its own database.
• Point a test at /tmp/movie-reviews.db or any file.
• Leave an environment variable set after a test.
• Depend on the order rows come back in unless the function promises one.

Check

dotnet test tests/Presentation.Tests.Integration