Load Testing Databases

Ed Elliott shares some tips on load testing a database:

Testing database performance is hard and takes a great deal of work to probably not even do particularly well. Instead of thinking about how you can load test a database think about how you can drive the application.

For instance, if you have a web app then use JMeter to simulate load. If you have a “fat app”, then you might need to write some code to call specific workflows through the application.

Click through for good advice, particularly around what you should not do.

Testing an Event-Driven System

Andy Chambers takes us through how to test an event-driven system:

Each distinct service has a nice, pure data model with extensive unit tests, but now with new clients (and consequently new requirements) coming thick and fast, the number of these services is rapidly increasing. The testing guardian angel who sometimes visits your thoughts during your morning commute has noticed an increase in the release of bugs that could have been prevented with better integration tests.

Finally after a few incidents in production, and with velocity slowing down due to the deployment pipeline frequently being clogged up by flaky integration tests, you start to think about what you want from your test suite. You set off looking for ideas to make really solid end-to-end tests. You wonder if it’s possible to make them fast. You think about all the things you could do with the time freed up by not having to apply manual data fixes that correct for deploying bad code.

At the end of it all, hopefully you’ll arrive here and learn about the Test Machine.

Check it out. Testing these types of system is certainly possible, but can be a bit difficult because of the additional layers of complexity.

Failing Pester Tests Can Still Show Green

Shane O’Neill walks us through an oopsie moment:

In modifying the template, I forgot to take out the original It block and just put my It block inside it.

This lead to my block “pass by deafult” failed 
(as it should cause of that typo) but the original, parent block it was in “does something useful” passed!

Click through for a demo and explanation.

Generating Workloads with Powershell

Rob Sewell wants to generate a workload against AdventureWorks using Powershell:

For a later blog post I have been trying to generate some workload against an AdventureWorks database.

I found this excellent blog post by Pieter Vanhove thttps://blogs.technet.microsoft.com/msftpietervanhove/2016/01/08/generate-workload-on-your-azure-sql-database/ which references this 2011 post by Jonathan Kehayias t
https://www.sqlskills.com/blogs/jonathan/the-adventureworks2008r2-books-online-random-workload-generator/

Rob turns these into multi-threaded workload generators. If you’re looking at generating stress on servers, you might also look at PigDog, developed by Mark Willkinson (one of my co-workers, so I have seen the look of joy on his face when he brings SQL Server to its knees).

Unit Testing R Code

Kevin Feasel

2019-03-15

R, Testing

John Mount points out that you don’t need special infrastructure to perform unit testing in R:

There seems to be a general (false) impression among non R-core developers that to run tests, R package developers need a test management system such as RUnit or testthat. And a further false impression that testthat is the only R test management system. This is in fact not true, as R itself has a capable testing facility in “R CMD check” (a command triggering R checks from outside of any given integrated development environment).

By a combination of skimming the R-manuals ( https://cran.r-project.org/manuals.html ) and running a few experiments I came up with a description of how R-testing actually works. And I have adapted the available tools to fit my current preferred workflow. This may not be your preferred workflow, but I have and give my reasons below.

Food for thought for any R developer.

Testing Cosmos DB’s REST API

Hasan Savran shows how we can test Cosmos DB’s REST API using Postman:

        You have many options to access to CosmosDB. Rest API is one of these options and it is the low level access way to Cosmos DB. You can customize all options of CosmosDB by using REST API. To customize the calls, and pass the required authorization information, you need to use http headers. There are many headers you can set depending on the operation you want to run in CosmosDB.  I am going to cover only the required headers here.

      In the following example, I am going to try to create a database in CosmosDB emulator by using the REST API. First let’s look at the required header fields for this request. These requirement applies to all other REST API calls too.

It’s a little more complicated than just posting to a URL and Hasan has you covered.

The Anatomy of a Pester Test

Shane O’Neill takes us through using Pester to test self-contained scripts:

Where things differ…
…could be when you try to accommodate different people and create a .ps1 file that both defines and calls a function. Self Contained scripts, if you would call them that.
Normally the reason that I’ve heard from this is you’re trying to help a non-technical minded person and they just want a file that they can open, hit “run”, and everything is done for them.
Have you ever tried to Pester test those files though? It’s not recommended, especially if your function removes or modifies objects.

Click through for a solution and read Shane’s update as well for a scenario where it doesn’t quite work as hoped.

Regression Testing With Pester

Ust Oldfield continues a series on Pester testing:

In a previous post, I gave an overview to regression tests. In this post, I will give a practical example of developing and performing regression tests with the Pester framework for PowerShell. The code for performing regression tests is written in PowerShell using the Pester Framework. The tests are run through Azure DevOps pipelines and are designed to test regression scenarios. The PowerShell scripts, which contain the mechanism for executing tests, rely upon receiving the actual test definitions from a metadata database. The structure of the metadata database will be exactly the same as laid out in the Integration Test post.

There’s a hefty test script here too, so check it out.

An Overview of Regression Testing

Ust Oldfield gives us a primer on regression testing:

There are a variety of methods and techniques that can be used in the design and execution of regression tests. These are:
– Retest All
– Test Selection
– Test Case Prioritisation

Regression testing is really nice to have in place because it keeps you from looking like a buffoon for accidentally reintroducing a bug you’ve previously quashed.

Generating Fake Data

Rich Benner shows us how to use the Faker library in Python to generate test data:

There are far more options when using Faker. Looking at the official documentation you’ll see the list of different data types you can generate as well as options such as region specific data.

Go have fun trying this, it’s a small setup for a large amount of time saved.

These types of tools can be great for generating a bunch of data but come with a couple of risks. One is that in the fake addresses Rich shows, ZIP codes don’t match their states at all, so if your application needs valid combos, it can cause issues. The other problem comes from distributions: generated data often gets created off of a uniform distribution, so you might not find skewness-related problems (e.g., parameter sniffing issues) strictly in your test data.

That said, easily generating test data is powerful and I don’t want to let the good be the enemy of the great.

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June 2019
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