Skip to main content

The Test in Test Match


There are times when getting a stakeholder to agree that there's a problem is not easy. Then there are times where, having found a stakeholder who accepts the existence of an issue, you have difficulty persuading them that it's important to find a solution to it now.  And then there are those times when, having found a sponsor who both recognises and wants to relieve the particular headache you've identified, they can't get past some narrow view of it - either in terms of the problem space or the complexity of the necessary solution or both - and you end up with incomplete fixes that might focus on a particular case or which will fail in logic for some subset of cases and perhaps even compromise the integrity of the implementation to boot.

Limited-overs cricket found itself in this position a few years ago. In this format of cricket the two teams each bat for one innings to try to score runs given a set number of balls bowled to them and within a set number of wickets (the number of players who can be out). When all the balls are bowled or all of the wickets are lost, the innings ends. Whichever team makes the most runs wins.

Unlike many other sports, cricket matches stop during rain and, if the rain lasts long enough, the match is reduced in length to ensure that it still fits into the day.  The cricketing authorities recognised the problem - how to perform that reduction fairly - and knew they needed a solution but, by the account in Duckworth Lewis: The Method and the Men behind it, failed to comprehend the range of scenarios that needed to be considered and were not prepared to think about the problem in anything other than a single dimension.

The case that preoccupied cricket was when it rained after team 1 (the first team to bat) had finished their innings but before team 2 started, or had completed, theirs. In the case where this reduced the number of balls that team 2 could face, they would simply scale the number of runs that team 2 had to make proportional to the number of balls. So, if team 1 made 100 in their innings, and team 2 only faced half as many balls as team 1 then they'd have to make half the total (plus one to win), i.e. 51. Which seems logical enough except that it doesn't take into account that team 2 still have as many wickets as team 1 had and so can take more risks without worrying about running out of wickets.

One key insight required here is that more then one parameter determines a fair rescaling of the total: both runs and number of wickets available are important. A second is that rain could occur at any point in the match, even forcing team 1 to receive fewer balls than they expected when they started their innings, if heavy rain falls during it. The rescaling needs to be fair to both teams and so needs to take into account the point in the innings at which the match was affected: if team 1 were cautious initially to preserve wickets, with the intention of being aggressive at the end of their innings, but then the innings is cut short they will feel aggreived because they could and would have been more aggressive had they known there were fewer balls to face.

Duckworth and Lewis are academics, statisticians and cricket lovers. Their book - which can be quite dry and occasionally petty, but is worth persevering with - details the original problem and a selection of sticking plasters that were applied to it. They show how broken methodologies implemented with apparently little thought or testing resulted in severe embarrassments such as a world cup match where South Africa's innings was reduced in length but their target was not (due to the then-current rules) and so instead of needing 22 runs from 13 balls they were rescaled to 22 runs from 1 ball, which is essentially impossible in the game.

The solution they proposed, the Duckworth Lewis Method, now in operation in cricket worldwide, introduces the notion of resource for a batting team which is generated from historical match data and takes into account the match position, the number of balls still to come and the number of wickets still standing. Under this system, the relative resources available to the teams when play is interrupted are used for scaling. For example, a team with many overs and wickets in hand will have a lot of resource; a team with the same number of overs but few wickets will have less because they would likely have to play more defensively to preserve their wickets.

In the book Duckworth and Lewis demonstrate the problem by highlighting a relatively small number of realistic scenarios in which unwanted results would occur - results which it was clear to the cricketing authorities would be travesties. They use these to enforce the message that a higher level of sophistication (than simply scaling based on number of balls) is required. They suggest a solution and describe it at a high level in terms that should be already familiar to their stakeholders. They, importantly, provide an implementation of the method that would be tractable too. (And over time they have refined the methodology so that its use during a match is now relatively streamlined.)

They discuss clearly and reasonably the relative advantages and disadvantages of their methods compared to others. They explain how some of the secondary stakeholders - the media in particular - seem unwilling to try to get their heads round the principles of the solution and what they've done to try to overcome that. They identify the weak spots that still exist in certain extreme scenarios and they suggest enhancements, some of which are rejected by the cricket authorities to Duckworth and Lewis's clear frustration. They address suggestions from third parties for the application of the method in situations it was not designed for, such as Test Match cricket, where the number of overs is not limited and explore other places it could be applied or extended to. And if that's not enough, they even provide a FAQ.

Let's not get into the is testing (a) science debate  here (although if you're interested...) but instead look at some relevant parallels with a testing role and the way that Duckworth and Lewis went about their business:
  • they analysed approaches using thought experiments and real data searching for the anomalous cases - cases not presented to them as problems by the stakeholders 
  • they communicated with their stakeholders and others in their own language to a relevant and realistic level of detail
  • they were and are open about their own approach and to other approaches, wanting to judge them all on a level playing field.
Image: http://flic.kr/p/6Pzxej

Comments

Popular posts from this blog

Enjoy Testing

  The testers at work had a lean coffee session this week. One of the questions was  "I like testing best because ..." I said that I find the combination of technical, intellectual, and social challenges endlessly enjoyable, fascinating, and stimulating. That's easy to say, and it sounds good too, but today I wondered whether my work actually reflects it. So I made a list of some of the things I did in the last working week: investigating a production problem and pairing to file an incident report finding problems in the incident reporting process feeding back in various ways to various people about the reporting process facilitating a cross-team retrospective on the Kubernetes issue that affected my team's service participating in several lengthy calibration workshops as my team merges with another trying to walk a line between presenting my perspective on things I find important and over-contributing providing feedback and advice on the process identifying a

Testing (AI) is Testing

Last November I gave a talk, Random Exploration of a Chatbot API , at the BCS Testing, Diversity, AI Conference .  It was a nice surprise afterwards to be offered a book from their catalogue and I chose Artificial Intelligence and Software Testing by Rex Black, James Davenport, Joanna Olszewska, Jeremias Rößler, Adam Leon Smith, and Jonathon Wright.  This week, on a couple of train journeys around East Anglia, I read it and made sketchnotes. As someone not deeply into this field, but who has been experimenting with AI as a testing tool at work, I found the landscape view provided by the book interesting, particularly the lists: of challenges in testing AI, of approaches to testing AI, and of quality aspects to consider when evaluating AI.  Despite the hype around the area right now there's much that any competent tester will be familiar with, and skills that translate directly. Where there's likely to be novelty is in the technology, and the technical domain, and the effect of

Notes on Testing Notes

Ben Dowen pinged me and others on Twitter last week , asking for "a nice concise resource to link to for a blog post - about taking good Testing notes." I didn't have one so I thought I'd write a few words on how I'm doing it at the moment for my work at Ada Health, alongside Ben. You may have read previously that I use a script to upload Markdown-based text files to Confluence . Here's the template that I start from: # Date + Title # Mission # Summary WIP! # Notes Then I fill out what I plan to do. The Mission can be as high or low level as I want it to be. Sometimes, if deeper context might be valuable I'll add a Background subsection to it. I don't fill in the Summary section until the end. It's a high-level overview of what I did, what I found, risks identified, value provided, and so on. Between the Mission and Summary I hope that a reader can see what I initially intended and what actually

The Great Post Office Scandal

  The Great Post Office Scandal by Nick Wallis is a depressing, dispiriting, and disheartening read. For anyone that cares about fairness and ethics in the relationship that business and technology has with individuals and wider society, at least. As a software tester working in the healthcare sector who has signed up to the ACM code of ethics through my membership of the Association for Software Testing I put myself firmly in that camp. Wallis does extraordinarily well to weave a compelling and readable narrative out of a years-long story with a large and constantly-changing cast and depth across subjects ranging from the intensely personal to extremely technical, and through procedure, jurisprudence, politics, and corporate governance. I won't try to summarise that story here (although Wikipedia takes a couple of stabs at it ) but I'll pull out a handful of threads that I think testers might be interested in: The unbelievable naivety which lead to Horizon (the system at th

Agile Testing Questioned

Zenzi Ali has been running a book club on the Association for Software Testing Slack and over the last few weeks we've read Agile Testing Condensed by Janet Gregory and Lisa Crispin. Each chapter was taken as a jumping off point for one or two discussion points and I really enjoyed the opportunity to think about the questions Zenzi posed and sometimes pop a question or two back into the conversation as well. This post reproduces the questions and my answers, lightly edited for formatting. --00-- Ten principles of agile testing are given in the book. Do you think there is a foundational principle that the others must be built upon? In your experience, do you find that some of these principles are less or more important than others?  The text says they are for a team wanting to deliver the highest-quality product they can. If we can regard a motivation as a foundational principle, perhaps that could be it: each of the ten pr

Leaps and Boundary Objects

Brian Marick  recently launched a new podcast, Oddly Influenced . I said this about it on Twitter: Boundary Objects, the first episode of @marick's podcast, is thought-provoking and densely-packed with some lovely turns of phrase. I played it twice in a row. Very roughly, boundary objects are things or concepts that help different interest groups to collaborate by being ambiguous enough to be meaningful and motivational to all parties. Wikipedia  elaborates, somewhat formally:  [boundary objects are] both plastic enough to adapt to local needs and constraints of the several parties employing them, yet robust enough to maintain a common identity across sites ... The creation and management of boundary objects is key in developing and maintaining coherence across intersecting social worlds. The podcast talks about boundary objects in general and then applies the idea to software development specifically, casting acceptance test

Where No-one Else Looks

In yesterday's post, Optimising start of your exploratory testing , Maaret Pyhäjärvi lists anti-patterns she's observed in testers that can lead to shallow outcomes of testing. She ends with this call: Go find (some of) what the others have missed! That strikes a chord. In Toujours Testing I recalled how my young daughter, in her self-appointed role as a Thing Searcher, had asked me how she could find things that no-one else finds. I replied Look where no-one else looks. Which made her happy, but also made me happy because that instinctive response externalised something that had previously been internal.  The phrase has stuck, too, and I recall it when I'm working. It doesn't mean targeting the obscure, although it can mean that.  It also doesn't mean not looking at areas that have previously been covered, although again it can mean that. More, for me, it is about seeking levels of granularity, or perspectives, or methods of engagement, or personas, or data, or im

Am I Wrong?

I happened across Exploratory Testing: Why Is It Not Ideal for Agile Projects? by Vitaly Prus this week and I was triggered. But why? I took a few minutes to think that through. Partly, I guess, I feel directly challenged. I work on an agile project (by the definition in the article) and I would say that I use exclusively exploratory testing. Naturally, I like to think I'm doing a good job. Am I wrong? After calming down, and re-reading the article a couple of times, I don't think so. 😸 From the start, even the title makes me tense. The ideal solution is a perfect solution, the best solution. My context-driven instincts are reluctant to accept the premise, and I wonder what the author thinks is an ideal solution for an agile project, or any project. I notice also that I slid so easily from "an approach is not ideal" into "I am not doing a good job" and, in retrospect, that makes me smile. It doesn't do any harm to be reminded that your cognitive bias

External Brains

A month or two ago, after seeing how I was taking notes and sharing information, a colleague pointed me at Tiego Forte's blog on Building a Second Brain : [BASB is] a methodology for saving and systematically reminding us of the ideas, inspirations, insights, and connections we’ve gained through our experience. It expands our memory and our intellect... That definitely sounded like my kind of thing so I ordered the upcoming book, waited for it to arrive, and then read it in a couple of sittings. Very crudely, I'd summarise it something like this: notes are atomic items, each one a single idea, and are not just textual notes should capture what your gut tells you could be valuable notes should capture what you think you need right now notes should preserve important context for restarting work notes on a topic are bundled in a folder for a Project, Area, or Resource and moved into Archive when they're done. ( PARA )

Binary Oppositions

I am totally loving Oddly Influenced, Brian Marick's new podcast. The latest episoide covers ways in which schools of thought and practice can inhibit the cross-fertilisation of ideas.  It includes a case study in experimental physics from Peter Galison's book, Image and Logic , where two different approaches to the same particle analysis problem seem to run on separate, parallel tracks: In the 'head to world' tradition, you use your head to carefully construct situations that allow the world to express its subtle truths ... In the 'world to head' tradition, you make yourself ever more sensitive to the world’s self-expressed truths ... The first of these wants to theorise and then craft an experiment using statistics while the latter wants to gather data and try to understand it visually. Marick is pessimistic about the scope for crossover in this kind of situation: How do you bridge traditions that differ on aesthetics, on different standards of what counts as