Critical Thinking for Testers

James Bach
http://www.satisfice.com
james@satisfice.com
Twitter: @jamesmarcusbach

Michael Bolton
http://www.developsense.com
michael@developsense.com
Twitter: @michaelbolton

Why Dont People Think Well?

blem:
Consider this pro

t$1.10.
Abatandballcos theball.
e ba tc os ts o ne dollarmorethan
Th
eballcost?
Howmuchdoesth
 Why Dont People Think Well?

Steveisveryshyandwithdrawn,invariablyhelpfulbut
withlittleinterestinpeopleorintheworldofreality.A
meekandtidysoul,hehasaneedfororderandstructure,
andapassionfordetail.

IsStevemorelikelytobe
alibrarian? afarmer?

Do you prefer A or B?

ImaginethattheUSispreparingfortheoutbreakofanunusual
Asiandisease,whichisexpectedtokill600people. Two
alternativeprogramstocombatthediseasehavebeen
proposed. Assumethattheexactscientificestimatesofthe
consequencesoftheprogramsareasfollows.

ProgramA: IfProgramAisadopted,200peoplewillbesaved.

ProgramB: IfProgramBisadopted,thereis1/3probability
that600peoplewillbesaved,and2/3probabilitythat
nopeoplewillbesaved.
 Do you prefer C or D?

Imaginetwomoreprogramstocombatthediseaseare
proposed:

ProgramC: IfProgramCisadopted,400peoplewilldie.

ProgramD: IfProgramDisadopted,thereis1/3probability
that600peoplewillbesaved,and2/3probabilitythat
nopeoplewillbesaved.

Reflex is IMPORTANT
But Critical Thinking is About Reflection

System 2
getmore suspend formal
logical debias
data m
g ju dgment odels
Slower thinkin solicit
r statistical
conside
REFLECTION
Surer review
t iv e s thinking
alterna

ics
norms habits cognitiveheurist
Faster REFLEX
Looser emotions priming
memorable inattentional
assumption coherence
s examples blindness

System 1
See Thinking Fast and Slow, by Daniel Kahneman
 Themes

Technology consists of complex and ephemeral

relationships that can seem simple, fixed,
objective, and dependable even when they arent.
Testers are people who ponder and probe
complexity.
Basic testing is a straightforward technical process.
But, excellent testing is a difficult social and
psychological process in addition to the technical
stuff.

The Nature of Critical Thinking

Critical thinking is purposeful, self-regulatory

judgment which results in interpretation, analysis,
evaluation, and inference, as well as explanation of
the evidential, conceptual, methodological,
criteriological, or contextual considerations upon
which that judgment is based. - Critical Thinking: A
Statement of Expert Consensus for Purposes of Educational
Assessment and Instruction, Dr. Peter Facione

(Critical thinking is, for the most part, about getting all the
benefits of your System 1 thinking reflexes while avoiding
self-deception and other mistakes.)
Boltons Definition of Critical Thinking

Michael Bolton

The Nature of Critical Thinking

We call it critical thinking whenever we
systematically doubt something that the signs tell
us is probably true. Working through the doubt
gives us a better foundation for our beliefs.
Critical thinking is a kind of de-focusing tactic,
because it requires you to seek alternatives to what
is already believed or what is being claimed.
Critical thinking is also a kind of focusing tactic,
because it requires you to analyze the specific
reasoning behind beliefs and claims.
 Why You Should Care

The Big Theme of This Workshop

Jerry Weinberg
 Dont
Graph of My Be A Turkey
Fantastic Life! Page 25!
(by the most intelligent Turkey in the world)
Every day the turkey adds one more data
point to his analysis proving that the farmer
LOVES turkeys.
Well Being!

Hundreds of observations DATA

ESTIMATED
support his theory. POSTHUMOUSLY
AFTER THANKSGIVING
Corn meal a little
Then, a few days before off today!
Thanksgiving

Based on a story told by Nassim Taleb, who stole it from

Bertrand Russell, who stole it from David Hume.

Dont Be A Turkey

No experience of the past can LOGICALLY

be projected into the future, because we have
no experience OF the future.
No big deal in a world of
stable, simple patterns.
BUT SOFTWARE IS NOT
STABLE OR SIMPLE.
PASSING TESTS CANNOT
PROVE SOFTWARE GOOD.
Based on a story told by Nassim Taleb, who stole it from
Bertrand Russell, who stole it from David Hume.
 How Do We Know What Is?

We know what is because we see what is.

We believe
we know what is because we see
what we interpret as signs that indicate
what is
based on our prior beliefs about the world.

How Do We Know What Is?

If I see X, then probably Y, because probably A, B, C, D, etc.

THIS CAN FAIL:

Getting into a car oops, not my car.
Bad driving Why?
Bad work Why?
Ignored people at my going away party Why?
Couldnt find soap dispenser in restroom Why?
Ordered orange juice at seafood restaurant waitress
misunderstood
 Remember this, you testers!

Exercise: Calculator Test

I was carrying a calculator.

I dropped it!
Perhaps it is damaged!
What might you do to test it?
 What prevents us
from asking questions?

What is an assumption?
 What makes an assumption
more dangerous?
1. Foundational: required to support critical plans and activities. (Changing the
assumption would change important behavior.)
2. Unlikely: may conflict with other assumptions or evidence that you have. (The
assumption is counter-intuitive, confusing, obsolete, or has a low probability of
being true.)
3. Blind: regards a matter about which you have no evidence whatsoever.
4. Controversial: may conflict with assumptions or evidence held by others. (The
assumption ignores controversy.)
5. Impolitic: expected to be declared, by social convention. (Failing to disclose the
assumption violates law or local custom.)
6. Volatile: regards a matter that is subject to sudden or extreme change. (The
assumption may be invalidated unexpectedly.)
7. Unsustainable: may be hard to maintain over a long period of time. (The
assumption must be stable.)
8. Premature: regards a matter about which you dont yet need to assume.
9. Narcotic: any assumption that comes packaged with assurances of its own safety.
10. Latent: Otherwise critical assumptions that we have not yet identified and dealt
with. (The act of managing assumptions can make them less critical.)

Models Link Observation and Inference

A model is an idea, activity, or object

such as an idea in your mind, a diagram, a list of words, a spreadsheet, a
person, a toy, an equation, a demonstration, or a program

that represents another idea, activity, or object

such as something complex that you need to work with or study.

whereby understanding the model may help you

understand or manipulate what it represents.
- A map helps navigate across a terrain.
- 2+2=4 is a model for adding two apples to a basket that already has two apples.
- Atmospheric models help predict where hurricanes will go.
- A fashion model helps understand how clothing would look on actual humans.
- Your beliefs about what you test are a model of what you test.
26
 Models Link Observation & Inference

Testers must distinguish

I believe observation from inference!
Our mental models form the
link between them
Defocusing is lateral thinking.
My Model Focusing is logical (or vertical)
of the World thinking.

I see 27

How many test case are needed to test the product

represented by this flowchart?
 Testing against requirements
is all about modeling.

The system shall operate at an input voltage

range of nominal 100 - 250 VAC.

Try it with an input voltage in the range of 100-250.

This is what people think you do

Compare the product to its specification

 This is more like what you really do

Compare the idea Compare the idea

of the product to of the product to
a description of it the actual product

Compare the actual product to a description of it

This is what you find

The designer INTENDS the product to

be Firefox compatible,
but never says so, and it actually is not.

The designer INTENDS the The designer INTENDS the product

product to be Firefox compatible, to be Firefox compatible,
SAYS SO IN THE SPEC, MAKES IT FIREFOX COMPATIBLE,
but it actually is not. but forgets to say so in the spec.
The designer
INTENDS
the product to be
Firefox compatible,
SAYS SO,
The designer assumes the product and IT IS. The designer assumes
is not Firefox compatible, and it the product is not Firefox compatible,
actually is not, but the and no one claims that it is,
ONLINE HELP SAYS IT IS. The designer assumes but it ACTUALLY IS.
the product is not
Firefox compatible,
but it ACTUALLY IS, and the
ONLINE HELP SAYS IT IS.
 How to Think Critically:
Slowing down to let System 2 wake up

You may not understand. (errors in

interpreting and modeling a situation,
communication errors)

What you understand may not be true.

(missing information, observations not made,
tests not run)

The truth may not matter, or may matter

much more than you think. (poor
understanding of risk)

To What Do We Apply Critical Thinking?

Words and Pictures

Causation
The Product
Design
Behavior
The Project
Schedule
Infrastructure
The Test Strategy
Coverage
Oracles
Procedures
 Huh?
Critical Thinking About Words

Among other things, testers question premises.

A suppressed premise is an unstated premise that an
argument needs in order to be logical.
A suppressed premise is something that should be
there, but isnt
(or is there, but its invisible or implicit.)
Among other things, testers bring suppressed
premises to light and then question them.
A diverse set of models can help us to see the things
that arent there.

35

Example: Missing Words

I performed the tests. All my tests passed.

Therefore, the product works.
The programmer said he fixed the bug. I
cant reproduce it anymore. Therefore it must
be fixed.
Microsoft Word frequently crashes while I am
using it. Therefore its a bad product.
Step 1. Reboot the test system.
Step 2. Start the application.
36
Example: Generating Interpretations

Selectively emphasize each word in a statement;

also consider alternative meanings.

MARY had a little lamb.

Mary HAD a little lamb.
Mary had A little lamb.
Mary had a LITTLE lamb.
Mary had a little LAMB.

37

Really?
Critical Thinking About Interpretation
 So?
Critical Thinking About Risk

When the user presses a button on the

touchscreen, the system shall respond within
300 milliseconds.

How would you test this?

Heuristic Model:
The Four-Part Risk Story

Someone may be hurt or annoyed

because of something that might go wrong while operating the product,
due to some vulnerability in the product
that is exploited by some threat.

Victim. Someone that experiences the impact of a problem. Ultimately

no bug can be important unless it victimizes a human.
Problem: Something the product does that we wish it wouldnt do.
Vulnerability: Something about the product that causes or allows it to
exhibit a problem, under certain conditions.
Threat: Some condition or input external to the product that, were it to
occur, would trigger a problem in a vulnerable product.
 Critical Thinking About Projects

You will have five weeks to test the product:

5 weeks

Safety Language
(epistemic modality)

A precise, circumspect style of speaking and

writing, intended to clarify the difference between
observation and inference
Informed by a determination to suspend
conclusions, certainty, and judgment
All conclusions are conclusions for now
Certainty isn't available
Judgment is always uncertain, and decisions about
quality are based on politics and emotions.
Emphasizes appropriate subjectivity
A form of tester self-defense
 Why Use Safety Language?
Helps to defend credibility and reputation
Precision and accuracy for our clients
Requires and helps to sharpen critical thinking
A qualifier circles back to you and changes your thinking.
Helps to prevent critical thinking errors
Fundamental attribution error
Cause-and-effect correlation
Lumping errors (assimilation bias)
Confirmation bias

The logical language of test framing is a form of safety language.

Words like if, or, else, unless, and so forth establish context and
preserve appropriate levels of uncertainty.
See http://www.developsense.com/blog/2010/09/test-framing/

Risks With Safety Language

To some, it sounds non-committal.

Done well, it prohibits you from being pinned down,
which some people will want to do.
Places responsibility for decisions in the hands of
those who should be making them; many find this
uncomfortable.
When you use safety language, you are sending a
social message that may have political and
emotional overtones.
Skillful use of safety language depends on knowing
when not to use it.
 Some Verbal Heuristics:
A vs. THE

Example: A problem instead of THE problem

Using A instead of THE helps us to avoid several
kinds of critical thinking errors
single path of causation
confusing correlation and causation
single level of explanation

Some Verbal Heuristics:

Unless

When someone asks a question based on a false

or incomplete premise, try adding unless to the
premise
When someone offers a Grand Truth about testing,
try appending unless or except in the case
ofor try countering with What if..?
 Some Verbal Heuristics:
And Also

The product gives the correct result! Yay!

It also may be silently deleting system files.

Some Verbal Heuristics:

So far and Not yet

The product works so far.

We havent seen it fail yet.
No customer has complained yet.
Remember: There is no test for ALWAYS.
 Some Verbal Heuristics:
Compared to what?

Software is too expensive!

Testing is taking too long!
We dont have enough information!

Critical Thinking About Diagrams

Analysis

[pointing at a box] What if the function in this box fails?

Can this function ever be invoked at the wrong time?
[pointing at any part of the diagram] What error checking do
you do here?
[pointing at an arrow] What exactly does this arrow mean?
What would happen if it was broken?

Browser Web Server

Database
Layer
App Server
 Guideword Heuristics
for Diagram Analysis

Boxes Lines Paths

Interfaces (testable) Missing/Drop-out Simplest
Missing/Drop-out Extra/Forking Popular
Extra/Interfering/Transient Incorrect Critical
Incorrect Complex
Timing/Sequencing
Timing/Sequencing Pathological
Status Communication
Contents/Algorithms Challenging
Data Structures
Conditional behavior Error Handling
Limitations Periodic
Error Handling

Browser Web Server

Database
Layer
App Server
Testability!

Critical Thinking About Timing

Event A

Event B

time

You want to test the interaction between two

potentially overlapping events.
What would you do to test them?
 Critical Thinking About Practices:
What does best practice mean?

Someone: Who is it? What do they know?

Believes: What specifically is the basis of their belief?
You: Is their belief applicable to you?
Might: How likely is the suffering to occur?
Suffer: So what? Maybe its worth it?
Unless: Really? Theres no alternative?
You do this practice: What does it mean to do it? What
does it cost? What are the side effects? What if you do it
badly? What if you do something else really well?

Beware of

Numbers: We cut test time by 94%.

Documentation: You must have a written plan.
Judgments: That project was chaotic. This project was a
success.
Behavior Claims: Our testers follow test plans.
Terminology: Exactly what is a test plan?
Contempt for Current Practice: CMM Level 1 (initial) vs.
CMM level 2 (repeatable)
Unqualified Claims: A subjective and unquantifiable
requirement is not testable.
 Look For

Context: This practice is useful when you want the power of

creative testing but you need high accountability, too.
People: The test manager must be enthusiastic and a real hands-on
leader or this wont work very well.
Skill: This practice requires the ability to tell a complete story about
testing: coverage, techniques, and evaluation methods.
Learning Curve: It took a good three months for the testers to
get good at producing test session reports.
Caveats: The metrics are useless unless the test manager holds
daily debriefings.
Alternatives: If you dont need the metrics, you ditch the daily
debriefings and the specifically formatted reports.
Agendas: I run a testing business, specializing in exploratory
testing.

Some Common Beliefs About Testing

Apply some critical thinking!

Every test must have an expected, predicted result.

Effective testing requires complete, clear, consistent, and
unambiguous specifications.
Bugs found earlier cost less to fix than bugs found later.
Testers are the quality gatekeepers for a product.
Repeated tests are fundamentally more valuable.
You cant manage what you cant measure.
Testing at boundary values is the best way to find bugs.
 Some Common Beliefs About Testing
Apply some critical thinking!
Test documentation is needed to deflect legal liability.
The more bugs testers find before release, the better the
testing effort.
Rigorous planning is essential for good testing.
Exploratory testing is unstructured testing, and is therefore
unreliable.
Adopting best practices will guarantee that we do a good
job of testing.
Step by step instructions are necessary to make testing a
repeatable process.

Some Common Thinking Errors

Reification Error
giving a name to a concept, and then believing it has an
objective existence in the world
ascribing material attributes to mental constructsthat
product has quality
mistaking relationships for thingsits purpose is
purpose and quality are relationships, not attributes;
they depend on the person
how can we count ideas? how can we quantify
relationships?
Some Common Thinking Errors

Fundamental Attribution Error

it always works that way; hes a jerk
failure to recognize that circumstance and context play a
part in behaviour and effects
The Similarity-Uniqueness Paradox
all companies are like ours; no companies are like
ours
failure to consider that everything incorporates
similarities and differences
Missing multiple paths of causation
A causes B (even though C and D are also required)

Some Common Thinking Errors

Assuming that effects are linear with causes

If we have 20% more traffic, throughput will slow by
20%
this kind of error ignores non-linearity and feedback
loopsc.f. general systems
Reactivity Bias
the act of observing affects the observed
a.k.a. Heisenbugs, the Hawthorne Effect
The Probabilistic Fallacy
confusing unpredictability and randomness
after the third hurricane hits Florida, is it time to relax?
Some Common Thinking Errors

Binary Thinking Error / False Dilemmas

all manual tests are bad; that idea never works
failure to consider gray areas; belief that something is
either entirely something or entirely not
Unidirectional Thinking
expresses itself in testing as a belief that the
application works
failure to consider the opposite: what if the application
fails?
to find problems, we need to be able to imagine that
they might exist

Some Common Thinking Errors

Availability Bias
the tendency to favor prominent or vivid instances in
making a decision or evaluation
example: people are afraid to fly, yet automobiles
are far more dangerous per passenger mile
to a tech support person (or to some testers), the
product always seems completely broken
spectacular failures often get more attention than
grinding little bugs
Confusing concurrence with correlation
A and B happen at the same time; they must be
related
Some Common Thinking Errors
Nominal Fallacies
believing that we know something well because we can
name it
equivalence classes
believing that we dont know something because we
dont have a name for it at our fingertips
the principle of concomitant variation;
inattentional blindness
Evaluative Bias of Language
failure to recognize the spin of word choices
or an attempt to game it
our product is full-featured; theirs is bloated

Some Common Thinking Errors

Selectivity Bias
choosing data (beforehand) that fits your preconceptions
or mission
ignoring data that doesnt fit
Assimilation Bias
modifying the data or observation (afterwards) to fit the
model
grouping distinct things under one conceptual umbrella
Jerry Weinberg refers to this as lumping
for testers, the risk is in identifying setup, pinpointing,
investigating, reporting, and fixing as testing
Some Common Thinking Errors

Narrative Bias
a.k.a post hoc, ergo propter hoc
explaining causation after the facts are in
The Ludic Fallacy
confusing complex human activities with random, roll-of-
the-dice games
Our project has a two-in-three chance of success
Confusing correlation with causation
When I change A, B changes; therefore A must be
causing B

Some Common Thinking Errors

Automation bias
people have a tendency to believe in results from an
automated process out of all proportion to validity
Formatting bias
Things are more credible when theyre on a nicely formatted
spreadsheet or document
Survivorship bias
we record and remember results from projects (or people)
who survived
The sailors survived because they prayed to Neptune.
What about the sailors who prayed and died anyway?
The bug rate for our successful projects was 0.2%
What was the bug rate for projects that were cancelled?
 Books on Testing
and Critical Thinking
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 Books on Testing
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