testing php applications

Risky Tests And Global State

Make Hidden Coupling Visible

Globals, superglobals, static properties, environment variables, current working directory, timezone, and process-level configuration can leak between tests. A test that passes alone but fails in the suite often has hidden shared state.

Use Strict Modes Deliberately

PHPUnit exposes command-line and XML configuration for strict output, global state, time limits, and risky-test failure handling. Enable strictness intentionally and fix the underlying coupling rather than relying on test order.

PHP example

<?php

declare(strict_types=1);

use PHPUnit\Framework\TestCase;

final class TimezoneTest extends TestCase
{
    private string $originalTimezone;

    protected function setUp(): void
    {
        $this->originalTimezone = date_default_timezone_get();
    }

    protected function tearDown(): void
    {
        date_default_timezone_set($this->originalTimezone);
    }

    public function testApplicationCanUseUtc(): void
    {
        date_default_timezone_set('UTC');

        $this->assertSame('UTC', date_default_timezone_get());
    }
}

tearDown() restores the process state even if an assertion fails. A try/finally block is another good choice when the change is local to one test.

Common Mistakes

Leaving changed timezone or environment variables behind.
Depending on test order.
Writing tests with no assertion or expectation.
Allowing unexpected output to hide debugging prints.

What To Practise

Recognise common sources of global state.
Restore process-level state after tests.
Use PHPUnit strict modes to expose risky tests.

Practice

Practice: Isolate A Timezone Test

Plan a test that changes the default timezone without affecting later tests.

Requirements

Capture the original timezone.
Restore it even if the test fails.
Explain why teardown or finally is appropriate.
Run the test in a different order mentally.

Show solution

A finally block protects later tests.

PHP example

<?php

declare(strict_types=1);

$original = date_default_timezone_get();

try {
    date_default_timezone_set('UTC');
    echo date_default_timezone_get() . PHP_EOL;
} finally {
    date_default_timezone_set($original);
}

echo date_default_timezone_get() === $original ? 'restored' : 'leaked';
echo PHP_EOL;

// Prints:
// UTC
// restored

PHPUnit setup and teardown hooks are often the natural home for this restoration.