Testing Absolute Units

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Welcome
Testing absolute units

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Photo by Moises Alex on Unsplash

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Photo by Stephen Andrews on Unsplash

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Uncertainty
Distrust
Opaqueness
High heart rate

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Consistency
Conﬁdence
Transparency
Low heart rate

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Knowing
Is the key

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Photo by Daniel Mingook Kim on Unsplash

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Learning
“In software development learning
is not a big part of the job. It is the
job.” – Woody Zuill
https://twitter.com/WoodyZuill/status/1502366061890473985

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@pelshoff
@pelshoff
Confidence
“Testing is all about conﬁdence.
When I'm working, I need to be
conﬁdent that I haven't broken
anything, and that the code that I
just wrote works as expected. When
I'm working, that's ALL I need to test
for.” – Allen Holub
https://twitter.com/allenholub/status/1538561251868954624

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@pelshoff
@pelshoff
Consider...
What is there to do?
What is left to do?
How should the system behave?
How should the component behave?
How should the component internals work?

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@pelshoff
Create...
Features
Feature
Scenario
Decomposition
Implementation

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@pelshoff
Transform
… to natural language spec
… to executable spec
… to integration test
… to unit test
… to code

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@pelshoff
Purity
Photo by Daniel Mingook Kim on Unsplash / Joke by XKCD on https://xkcd.com/435/

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@pelshoff
Natural language spec
User stories, story map, example map…

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Executable spec
Agree with three “it works, for me”

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@pelshoff
@pelshoff
/tests/features/Policy/Adjustment/nonSchemeMta.feature
Feature: non-scheme mid-term adjustments
In order to match my insurance policy to my evolved situation
As an insured party
I want to adjust my policy mid-term
Scenario: Annualised (full term) mta
Given a non-scheme policy
And the start date is "2019-01-01"
And the premium is 365 GBP
And the policy is bound
And the policy is opened
When the effective date is "2019-07-01"
And the mta is 375 GBP annualised
Then delta gross premium should be 5.04 GBP
Scenario: Pro rated mta
...
Photo by Osman Rana on Unsplash

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@pelshoff
Insurance
We sell it

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@pelshoff
@pelshoff
What is a non-scheme mid
term adjustment?
● Scheme: We sell an insurance product on behalf of an insurance company (underwriter)
● Non-scheme: We sell an insurance product the insurance company sells (broker)
● Policy: A contract between a customer and us that said customer is covered for certain perils
pertaining exposures for certain periods of time
● Term: One of a certain period of time, usually either a month or a year
● Mid term adjustment: an adjustment while a term is ongoing
● Effective date: The date this “version” if the policy goes live
● Premium: The fee a customer pays...
● Term premium: for all transactions combined
● Current premium: for the latest transaction of a would be term
● Delta premium: for the latest transaction..?

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@pelshoff
@pelshoff
What is a non-scheme mid
term adjustment?
● Non-scheme: We don’t decide the premium
● Mid term adjustment: for this adjustment to the contract
● Premium: and insurance companies might give us current ór delta
● Current premium: where current is the price for a full term (and for the next term upon renewal)
● Delta premium: and delta is ehm

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@pelshoff
@pelshoff
What is a delta premium?
● You pay 365GBP for a one year policy
● You change to a 375GBP premium half-way through
● The delta is NOT 10GBP
● You’ve paid 365 / ~2 too much
● You’ve paid 375 / ~2 too little
● 375 / ~2 - 365 / ~2 = ?
● ~187.5 - ~182.5 = 5.04

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@pelshoff
@pelshoff
/tests/features/Policy/Adjustment/nonSchemeMta.feature
As an insured party

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@pelshoff
@pelshoff
.../nonSchemeMta.feature | .../NonSchemeMtaContext.php
/**
* @Given /^the start date is
"2019\-01\-01"$/
*/
public function theStartDateIs
($arg1)
{
throw new PendingException()
;
}
/**
* @Given the start date is :aDate
*/
($aDate)
{
throw new PendingException()
;
}

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@pelshoff
@pelshoff
behat.yml
default:
suites:
Policy:
contexts:
- TestingAbsoluteUnits\Tests\Features\Policy\Adjustment\NonSchemeMtaContext
paths:
- ./tests/Features/Policy

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@pelshoff
@pelshoff
/**
* @Given the start date is :aDate
*/
($aDate)
{
$this->policy->updateStartDate
(
LocalDate::
parse(
trim(
$aDate, '"')
)
);
}

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@pelshoff
@pelshoff
Then delta gross premium should be
5.04 GBP
**
* @Then delta gross premium should be
:amount :currency
*/
public function deltaGrossPremiumShouldBe
(
$amount,
$currency
){
$this->policy->assertRecorded
(
new PremiumTransacted(
Money::
GBP(5_04)
)
);
}

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@pelshoff
@pelshoff
Terminal
$ vendor/bin/behat
As an insured party
TODO: write pending definition
1 scenario (1 pending)
8 steps (1 pending, 7 skipped)

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@pelshoff
@pelshoff
Terminal
$ vendor/bin/behat
1 scenario (1 failed)
8 steps (7 passed, 1 failed)

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@pelshoff
@pelshoff
Terminal
$ vendor/bin/behat
1 scenario (1 passed)
8 steps (8 passed)

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@pelshoff
I’m done!
and I can prove it

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@pelshoff
@pelshoff
/tests/Features/Policy/Adjustment/NonSchemeMtaTest.php
/**
* In order to match my insurance policy to my evolved situation
* As an insured party
* I want to adjust my policy mid-term
*/
public function it_calculates_non_scheme_mta_annualised
(): void
{
Policy::fake()
->givenNonSchemePolicy
()
->givenStartDateIs
(2019, 1, 1)
->givenPremiumIs
(365, 'GBP')
->givenPolicyIsBound
()
->givenPolicyIsOpened
()
->whenEffectiveDateIs
(2019, 7, 1)
->whenMtaIs(375, 'GBP', 'annualised')
->thenDeltaGrossPremiumShouldBe
(5.04, 'GBP');
}

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@pelshoff
@pelshoff
Heuristics
Don’t put too many (unimportant) details in feature tests
Keep the tests high-level

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@pelshoff
Design
Driven mad by tests

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@pelshoff
@pelshoff
Top 5 challenges with tests
5. Scope mix-up
4. Mocks
3. Too much, inconsistent or non-deterministic setup
2. No tests
1. Other devs
Photo by Matt Cramblett on Unsplash

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@pelshoff
@pelshoff
Top 5 challenges with tests
5. Scope mix-up
4. Mocks
3. Too much, inconsistent or non-deterministic setup
2. No tests
1. Other devs Design of the “Unit”

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@pelshoff
Unit
of decomposition

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@pelshoff
@pelshoff
class PremiumCalculation
{
public function act(PremiumCalculationAction $action): static
{
$action->assertActionCanBeApplied
($this->transactions, $this->period);
return $this->withTransaction
($action->transact($this->transactions, $this->period));
}
public function correct(PremiumCalculationCorrection $correction): static
{
$this->transactions->assertThereAreTransactions
();
$correction->assertCorrectionCanBeApplied
($this->transactions, $this->period);
$correctedCalculation = $this->withTransaction
(
LastTransactionPremiumReversal::
for($this->transactions)
);
return $correctedCalculation
->withTransaction
(
CorrectionTransaction::
fromTransaction(
$correction->transact($correctedCalculation
->transactions, $this->period)
)
);
}
}
src/Premium/PremiumCalculation.php

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@pelshoff
@pelshoff
/** @test */
public function can_adjust()
{
$bindPremium = new SinglePremium(Money::
GBP(365_00), ...);
$adjustPremium = new SinglePremium(Money::
GBP(375_00), ...);
$deltaPremium = new SinglePremium(Money::
GBP(5_04), ...);
$expected = Transactions::
of([
new PremiumTransaction(LocalDate::
of(2019, 1, 1), $bindPremium, $bindPremium),
of(2019, 7, 1), $adjustPremium
, $deltaPremium),
]);
$actual = Transactions::
of(
PremiumCalculation::
for(TermPeriod::of(...))
->act(new CurrentPremiumBind(
$bindPremium))
->act(new CurrentPremiumAdjustment(LocalDate::
))
->newTransactions
()
);
$this->assertEquals($expected, $actual);
}
tests/Premium/PremiumCalculationTest.php

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@pelshoff
What’s special
about this?

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@pelshoff
@pelshoff
class PremiumCalculationTest extends TestCase
{
public function is_immutable(){}
public function wont_bind_when_there_are_already_transactions
(){}
public function can_bind(){}
public function needs_existing_transactions_before_adjusting
(){}
public function can_adjust(){}
public function can_bind_then_adjust_multiple_times
(){}
public function can_correct_a_bind
(){}
public function wont_correct_with_a_new_bind_if_an_adjustment_happened
(){}
public function can_correct_an_adjustment
(){}
}
tests/Premium/...

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@pelshoff
@pelshoff
class PremiumCalculationTest extends TestCase
{
public function is_immutable(){}
public function can_bind_then_adjust_multiple_times
(){}
public function can_correct_a_bind
(){}
public function wont_correct_with_a_new_bind_if_an_adjustment_happened
(){}
public function can_correct_an_adjustment
(){}
}
class CurrentPremiumAdjustmentTest extends TestCase
{
public function needs_existing_transactions
(){}
public function can_only_append_transactions
(){}
public function must_be_within_term_bounds
(){}
public function can_adjust_to_a_higher_current_premium
(){}
public function can_adjust_to_a_lower_current_premium
(){}
public function can_adjust_on_the_first_day
(){}
public function can_adjust_on_the_final_day
(){}
}
class TransactionsTest extends TestCase
{
public function can_determine_term_premium
(){}
}
tests/Premium/...

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@pelshoff
@pelshoff
$ vendor/bin/phpunit --testdox
Premium Calculation (Tests\...\PremiumCalculation)
✔ Is immutable
✔ Can bind then adjust multiple times
✔ Can correct a bind
✔ Wont correct with a new bind if an adjustment happened
✔ Can correct an adjustment
Current Premium Adjustment (Tests\...\CurrentPremiumAdjustment)
✔ Needs existing transactions
✔ Can only append transactions
✔ Must be within term bounds
✔ Can adjust to a higher current premium
✔ Can adjust to a lower current premium
✔ Can adjust on the first day
✔ Can adjust on the final day
Transactions (Tests\...\Transactions)
✔ Can determine term premium
Terminal

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@pelshoff
@pelshoff
1. Fix the feature test
2. Fix the integration test
3. Fix the unit test
4. Fix the integration test
5. Fix the feature test
1. Make it work
2. Make it beautiful
3. (Make it fast)
Executable to-do list

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@pelshoff
@pelshoff
/** @test */
{
GBP(365_00), ...);
GBP(375_00), ...);
GBP(5_04), ...);
of([
, $deltaPremium),
]);
of(
$bindPremium))
))
->newTransactions
()
);
}

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@pelshoff
@pelshoff
Error : Class "TestingAbsoluteUnits\Tests\Unit\PremiumCalculation" not found
Error : Call to undefined method TestingAbsoluteUnits\Premium\PremiumCalculation::forTerm()
Error : Call to undefined method TestingAbsoluteUnits\Premium\PremiumCalculation::act(), etc.
TypeError : TestingAbsoluteUnits\Premium\PremiumCalculation::act(): Argument #1 ($param) must be of type
TestingAbsoluteUnits\Tests\Unit\CurrentPremiumAdjustment,
TestingAbsoluteUnits\Premium\Adjustment\CurrentPremiumAdjustment given
PremiumCalculation::newTransactions(): Return value must be of type array, null returned
Failed asserting that two objects are equal.

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@pelshoff
@pelshoff
/** @test */
{
GBP(365_00), ...);
GBP(375_00), ...);
GBP(5_04), ...);
of([
, $deltaPremium),
]);
of(
$bindPremium))
))
->newTransactions
()
);
}

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@pelshoff
@pelshoff
[] vs. [0 => PremiumTransaction Object (), 1 => PremiumTransaction Object ()]
[...] vs. [..., 1 => PremiumTransaction Object ()]
Error : Call to undefined method TestingAbsoluteUnits\Premium\Adjustment\CurrentPremiumAdjustment::transact()
[..., ...37500...] vs. [..., ...504...]
The form of the results is now the same. What’s next?

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@pelshoff
What’s hard
about this?

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@pelshoff
@pelshoff
/** @test */
public function can_adjust_to_a_higher_current_premium
()
{
GBP(365_00), ...);
GBP(375_00), ...);
GBP(5_04), ...);
$bindDate = LocalDate::of(2019, 1, 1);
$adjustDate = LocalDate::of(2019, 7, 1);
$adjustment = new CurrentPremiumAdjustment(
$adjustDate, $adjustPremium
);
$expected = new PremiumTransaction(
$adjustDate, $adjustPremium
, $deltaPremium);
$actual = $adjustment->transact(
Transactions::
fromBind($bindDate, $bindPremium),
TermPeriod::fullYearOf($adjustDate)
);
}
tests/Premium/Calculation/Adjustment/CurrentPremiumAdjustmentTest.php

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@pelshoff
@pelshoff
public function transact(Transactions $transactions, TermPeriod $period): Transaction
{
// Given the number of days we have left
// Take what we've paid so far
// Subtract what we've paid too much for the old policy
// Add what we pay for the new policy
$effectiveNumberOfDaysForNewCurrentPremium = $this->effectiveDate->
daysUntil
($period->exclusiveEndDate
());
$deltaPremium = $transactions->termPremium()
->multiply($period->fullTermDays())
->subtract(
$transactions
->currentPremium
()
->
multiply($effectiveNumberOfDaysForNewCurrentPremium
)
)
->add($this->premium->multiply($effectiveNumberOfDaysForNewCurrentPremium
))
->divide($period->fullTermDays())
->subtract($transactions->termPremium());
return new PremiumTransaction(
$this->effectiveDate, $this->premium, $deltaPremium);
}
src/Premium/Calculation/Adjustment/CurrentPremiumAdjustment.php

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@pelshoff
@pelshoff
Heuristics
A unit is a component you can test in isolation; Write tests with isolation and no mocks to create units
Fight the urge to automate and/or abstract test set-up; if it’s hard make it smaller
Large units are hard to TDD; if it’s hard make it smaller
Keep your suite fast and Run The Tests
Use test failures as a to-do list
Highlight what’s special
Highlight what’s hard

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@pelshoff
Test quality
Is your code writing checks that your tests can’t
cache?

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@pelshoff
@pelshoff
sum.php | sumTest.php
function sum(int $x, int $y) {
return $x + $y;
}
$this->assertEquals(4, sum(2, 2));
Photo by Maksym Kaharlytskyi on Unsplash

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@pelshoff
@pelshoff
divide.php | divideTest.php
function divide(int $x, int $y): float
{
return $x / $y;
}
$this->assertEquals(2, divide(4, 2));

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@pelshoff
@pelshoff
{
if ($y === 0) {
throw new DivisorFail();
}
return $x / $y;
}
$this->expectException
(
DivisorFail::
class
);
divide(1, 0);

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@pelshoff
@pelshoff
Transactions.php | TransactionsTest.php
public function sum(): int
{
if (count($this->transactions) <= 0) {
return 0;
}
return array_reduce(
$this->transactions,
fn(int $sum, int $transaction) =>
$sum + $transaction,
0
);
}
public function it_sums_to_zero
(): void
{
$transactions = new Transactions([])
;
$this->assertEquals(
0,
$transactions
->sum()
);
}
public function it_sums_good(): void
{
$transactions = new Transactions(
[3,4,5]
);
12,
$transactions
->sum()
);
}

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@pelshoff
@pelshoff
Terminal
$ XDEBUG_MODE=coverage vendor/bin/infection
.: killed, M: escaped, U: uncovered, E: fatal error, X: syntax error, T: timed out, S: skipped, I:
ignored
M........ (9 / 9)
9 mutations were generated:
8 mutants were killed
0 mutants were configured to be ignored
0 mutants were not covered by tests
1 covered mutants were not detected
0 errors were encountered
0 syntax errors were encountered
0 time outs were encountered
0 mutants required more time than configured
Metrics:
Mutation Score Indicator (MSI): 88%
Mutation Code Coverage: 100%
Covered Code MSI: 88%
Please note that some mutants will inevitably be harmless (i.e. false positives).

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@pelshoff
@pelshoff
infection.log
Escaped mutants:
================
1) Transactions.php:17 [M] LessThanOrEqualTo
--- Original
+++ New
@@ @@
}
public function sum() : int
{
- if (count($this->transactions) <= 0) {
+ if (count($this->transactions) < 0) {
return 0;
}
return array_reduce($this->transactions, fn(int $sum, int $transaction) => $sum +
$transaction, 0);
}
}

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@pelshoff
@pelshoff
Transactions.php | TransactionsTest.php
public function sum(): int
{
if (count($this->transactions) <= 0) {
return 0;
}
return array_reduce(
$this->transactions,
fn(int $sum, int $transaction) =>
$sum + $transaction,
0
);
}
public function it_sums_to_zero
(): void
{
$transactions = new Transactions([])
;
0,
$transactions
->sum()
);
}
public function it_sums_good(): void
{
$transactions = new Transactions(
[3,4,5]
);
12,
$transactions
->sum()
);
}

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@pelshoff
@pelshoff
infection.json
{
"$schema": "vendor/infection/infection/resources/schema.json"
,
"testFrameworkOptions": "--testsuite=Infection",
"source": {
"directories": [
"app"
]
},
"mutators": {
"@default": true,
"@cast": false
},
"logs": {
"text": "infection.log"
}
}
$ XDEBUG_MODE=coverage vendor/bin/infection --only-covered

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@pelshoff
Production code
Tests
Mutations

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@pelshoff
@pelshoff
Infection
Mutation testing lib for PHP
Analyses source tree and runs your suite for each applied mutation
Prefer regular PHPUnit TestCase for performance reasons
Run on entire suite or on changed ﬁles only
© Markus Schirp (https://twitter.com/_m_b_j_)

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@pelshoff
@pelshoff
Infection
On my M1 Macbook
86 test cases
Infection running with --only-covered for 128 mutants
\PHPUnit\TestCase: 0.057s
Infection: 14s
\Illuminate\Foundation\Testing\TestCase: 4.712s
Infection: 48s

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@pelshoff
@pelshoff
{
return $x / $y;
}
$this->assertEquals(2, divide(4, 2));

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@pelshoff
@pelshoff
{
return $x / $y;
}
use Eris\Generators
;
use Eris\TestTrait
;
$this->forAll(
Generators::
int(),
Generators::
int()
)
->then(fn(int $x, int $y) =>
$this->assertIsNumeric
(
divide(
$x, $y))
);
OutOfBoundsException : Evaluation ratio
0.01 is under the threshold 0.5
Caused by
DivisionByZeroError: Division by zero
Reproduce with:
ERIS_SEED=1646663840606414
vendor/bin/phpunit --filter '...'

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@pelshoff
@pelshoff
Eris
Property testing lib for PHP
“Brute forces” towards edge cases
Prefer regular PHPUnit TestCase for performance reasons

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@pelshoff
@pelshoff

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@pelshoff
|u|

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@pelshoff

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@pelshoff
Pim Elshoff
twitter.com/pelshoff
[email protected]
speakerdeck.com/pelshoff
Testing Absolute Units

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Testing Absolute Units

Testing Absolute Units

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