diff --git a/tests/Facade/ConstantBackOffTest.php b/tests/Facade/ConstantBackOffTest.php
index bb091bb..22456d4 100644
--- a/tests/Facade/ConstantBackOffTest.php
+++ b/tests/Facade/ConstantBackOffTest.php
@@ -3,7 +3,6 @@
 namespace Orangesoft\BackOff\Tests\Facade;
 
 use PHPUnit\Framework\TestCase;
-use Orangesoft\BackOff\BackOffInterface;
 use Orangesoft\BackOff\Facade\ConstantBackOff;
 use Orangesoft\BackOff\Jitter\DummyJitter;
 use Orangesoft\BackOff\Sleeper\Sleeper;
@@ -20,8 +19,6 @@ public function testBackOff(): void
 
         $backOff = new ConstantBackOff($maxAttempts, $baseTimeMs, $capTimeMs, $jitter, $sleeper);
 
-        $this->assertInstanceOf(BackOffInterface::class, $backOff);
-
         $this->expectException(\RuntimeException::class);
 
         $backOff->backOff(0, new \RuntimeException());
diff --git a/tests/Facade/DecorrelationJitterBackOffTest.php b/tests/Facade/DecorrelationJitterBackOffTest.php
index b7a447f..dec2406 100644
--- a/tests/Facade/DecorrelationJitterBackOffTest.php
+++ b/tests/Facade/DecorrelationJitterBackOffTest.php
@@ -3,7 +3,6 @@
 namespace Orangesoft\BackOff\Tests\Facade;
 
 use PHPUnit\Framework\TestCase;
-use Orangesoft\BackOff\BackOffInterface;
 use Orangesoft\BackOff\Facade\DecorrelationJitterBackOff;
 use Orangesoft\BackOff\Sleeper\Sleeper;
 
@@ -19,8 +18,6 @@ public function testBackOff(): void
 
         $backOff = new DecorrelationJitterBackOff($maxAttempts, $baseTimeMs, $capTimeMs, $multiplier, $sleeper);
 
-        $this->assertInstanceOf(BackOffInterface::class, $backOff);
-
         $this->expectException(\RuntimeException::class);
 
         $backOff->backOff(0, new \RuntimeException());
diff --git a/tests/Facade/ExponentialBackOffTest.php b/tests/Facade/ExponentialBackOffTest.php
index 9ff6a4a..fc7948e 100644
--- a/tests/Facade/ExponentialBackOffTest.php
+++ b/tests/Facade/ExponentialBackOffTest.php
@@ -3,7 +3,6 @@
 namespace Orangesoft\BackOff\Tests\Facade;
 
 use PHPUnit\Framework\TestCase;
-use Orangesoft\BackOff\BackOffInterface;
 use Orangesoft\BackOff\Facade\ExponentialBackOff;
 use Orangesoft\BackOff\Jitter\DummyJitter;
 use Orangesoft\BackOff\Sleeper\Sleeper;
@@ -21,8 +20,6 @@ public function testBackOff(): void
 
         $backOff = new ExponentialBackOff($maxAttempts, $baseTimeMs, $capTimeMs, $multiplier, $jitter, $sleeper);
 
-        $this->assertInstanceOf(BackOffInterface::class, $backOff);
-
         $this->expectException(\RuntimeException::class);
 
         $backOff->backOff(0, new \RuntimeException());
diff --git a/tests/Facade/LinearBackOffTest.php b/tests/Facade/LinearBackOffTest.php
index d28cb1e..5ddee96 100644
--- a/tests/Facade/LinearBackOffTest.php
+++ b/tests/Facade/LinearBackOffTest.php
@@ -3,7 +3,6 @@
 namespace Orangesoft\BackOff\Tests\Facade;
 
 use PHPUnit\Framework\TestCase;
-use Orangesoft\BackOff\BackOffInterface;
 use Orangesoft\BackOff\Facade\LinearBackOff;
 use Orangesoft\BackOff\Jitter\DummyJitter;
 use Orangesoft\BackOff\Sleeper\Sleeper;
@@ -20,8 +19,6 @@ public function testBackOff(): void
 
         $backOff = new LinearBackOff($maxAttempts, $baseTimeMs, $capTimeMs, $jitter, $sleeper);
 
-        $this->assertInstanceOf(BackOffInterface::class, $backOff);
-
         $this->expectException(\RuntimeException::class);
 
         $backOff->backOff(0, new \RuntimeException());
diff --git a/tests/Generator/GeneratorBuilderTest.php b/tests/Generator/GeneratorBuilderTest.php
index 5f9f58b..4f925e6 100644
--- a/tests/Generator/GeneratorBuilderTest.php
+++ b/tests/Generator/GeneratorBuilderTest.php
@@ -6,80 +6,77 @@
 use Orangesoft\BackOff\Generator\Generator;
 use Orangesoft\BackOff\Generator\GeneratorBuilder;
 use Orangesoft\BackOff\Duration\Milliseconds;
-use Orangesoft\BackOff\Duration\DurationInterface;
-use Orangesoft\BackOff\Strategy\ConstantStrategy;
+use Orangesoft\BackOff\Strategy\ExponentialStrategy;
 use Orangesoft\BackOff\Strategy\LinearStrategy;
-use Orangesoft\BackOff\Strategy\StrategyInterface;
 use Orangesoft\BackOff\Jitter\DummyJitter;
 use Orangesoft\BackOff\Jitter\FullJitter;
-use Orangesoft\BackOff\Jitter\JitterInterface;
 
 class GeneratorBuilderTest extends TestCase
 {
     public function testCreate(): void
     {
-        $builder = GeneratorBuilder::create();
+        $generatorBuilder = GeneratorBuilder::create();
 
-        $this->assertInstanceOf(GeneratorBuilder::class, $builder);
+        $this->assertInstanceOf(GeneratorBuilder::class, $generatorBuilder);
     }
 
-    public function testDefaults(): void
+    public function testDefault(): void
     {
-        $builder = GeneratorBuilder::create();
+        $generatorBuilder = GeneratorBuilder::create();
 
-        $this->assertSame(INF, $builder->getMaxAttempts());
-        $this->assertEquals(1000, $builder->getBaseTime()->asMilliseconds());
-        $this->assertEquals(60 * 1000, $builder->getCapTime()->asMilliseconds());
-        $this->assertInstanceOf(ConstantStrategy::class, $builder->getStrategy());
-        $this->assertInstanceOf(DummyJitter::class, $builder->getJitter());
+        $this->assertSame(INF, $generatorBuilder->getMaxAttempts());
+        $this->assertEquals(1000, $generatorBuilder->getBaseTime()->asMilliseconds());
+        $this->assertEquals(60 * 1000, $generatorBuilder->getCapTime()->asMilliseconds());
+        $this->assertInstanceOf(ExponentialStrategy::class, $generatorBuilder->getStrategy());
+        $this->assertInstanceOf(DummyJitter::class, $generatorBuilder->getJitter());
     }
 
     public function testMaxAttempts(): void
     {
-        $builder = GeneratorBuilder::create()->setMaxAttempts(3);
+        $generatorBuilder = GeneratorBuilder::create()->setMaxAttempts(3);
 
-        $this->assertEquals(3, $builder->getMaxAttempts());
+        $this->assertEquals(3, $generatorBuilder->getMaxAttempts());
     }
 
     public function testMaxAttemptsInf(): void
     {
-        $builder = GeneratorBuilder::create()->setMaxAttempts(INF);
+        $generatorBuilder = GeneratorBuilder::create()->setMaxAttempts(INF);
 
-        $this->assertEquals(INF, $builder->getMaxAttempts());
+        $this->assertEquals(INF, $generatorBuilder->getMaxAttempts());
     }
 
     public function testBaseTime(): void
     {
-        $builder = GeneratorBuilder::create()->setBaseTime(new Milliseconds(1000));
+        $generatorBuilder = GeneratorBuilder::create()->setBaseTime(new Milliseconds(1000));
 
-        $this->assertInstanceOf(DurationInterface::class, $builder->getBaseTime());
+        $this->assertInstanceOf(Milliseconds::class, $generatorBuilder->getBaseTime());
     }
 
     public function testCapTime(): void
     {
-        $builder = GeneratorBuilder::create()->setCapTime(new Milliseconds(1000));
+        $generatorBuilder = GeneratorBuilder::create()->setCapTime(new Milliseconds(1000));
 
-        $this->assertInstanceOf(DurationInterface::class, $builder->getCapTime());
+        $this->assertInstanceOf(Milliseconds::class, $generatorBuilder->getCapTime());
     }
 
     public function testStrategy(): void
     {
-        $builder = GeneratorBuilder::create()->setStrategy(new LinearStrategy());
+        $generatorBuilder = GeneratorBuilder::create()->setStrategy(new LinearStrategy());
 
-        $this->assertInstanceOf(StrategyInterface::class, $builder->getStrategy());
+        $this->assertInstanceOf(LinearStrategy::class, $generatorBuilder->getStrategy());
     }
 
     public function testJitter(): void
     {
-        $builder = GeneratorBuilder::create()->setJitter(new FullJitter());
+        $generatorBuilder = GeneratorBuilder::create()->setJitter(new FullJitter());
 
-        $this->assertInstanceOf(JitterInterface::class, $builder->getJitter());
+        $this->assertInstanceOf(FullJitter::class, $generatorBuilder->getJitter());
     }
 
     public function testBuild(): void
     {
-        $generator = GeneratorBuilder::create()->build();
+        $generatorBuilder = GeneratorBuilder::create()->build();
 
-        $this->assertInstanceOf(Generator::class, $generator);
+        $this->assertInstanceOf(Generator::class, $generatorBuilder);
     }
 }
diff --git a/tests/Generator/GeneratorTest.php b/tests/Generator/GeneratorTest.php
index ebf0bc0..c8a85dd 100644
--- a/tests/Generator/GeneratorTest.php
+++ b/tests/Generator/GeneratorTest.php
@@ -5,7 +5,6 @@
 use PHPUnit\Framework\TestCase;
 use Orangesoft\BackOff\Generator\GeneratorBuilder;
 use Orangesoft\BackOff\Duration\Milliseconds;
-use Orangesoft\BackOff\Duration\DurationInterface;
 use Orangesoft\BackOff\Strategy\LinearStrategy;
 use Orangesoft\BackOff\Generator\Exception\MaxAttemptsException;
 
@@ -22,8 +21,6 @@ public function testGenerate(): void
 
         $duration = $generator->generate(3);
 
-        $this->assertInstanceOf(DurationInterface::class, $duration);
-
         $this->assertEquals(4000, $duration->asMilliseconds());
     }
 
diff --git a/tests/Jitter/FullJitterTest.php b/tests/Jitter/FullJitterTest.php
index b1e3911..2f0ead6 100644
--- a/tests/Jitter/FullJitterTest.php
+++ b/tests/Jitter/FullJitterTest.php
@@ -10,9 +10,9 @@ class FullJitterTest extends TestCase
 {
     public function testJitter(): void
     {
-        $equalJitter = new FullJitter();
+        $fullJitter = new FullJitter();
 
-        $duration = $equalJitter->jitter(new Milliseconds(1000));
+        $duration = $fullJitter->jitter(new Milliseconds(1000));
 
         $this->assertGreaterThanOrEqual(0, $duration->asMilliseconds());
         $this->assertLessThanOrEqual(1000, $duration->asMilliseconds());
diff --git a/tests/Retry/BackOffCounter.php b/tests/Retry/AttemptsCounter.php
similarity index 80%
rename from tests/Retry/BackOffCounter.php
rename to tests/Retry/AttemptsCounter.php
index 9fe3884..ac47350 100644
--- a/tests/Retry/BackOffCounter.php
+++ b/tests/Retry/AttemptsCounter.php
@@ -4,21 +4,21 @@
 
 use Orangesoft\BackOff\BackOffInterface;
 
-class BackOffCounter implements BackOffInterface
+class AttemptsCounter implements BackOffInterface
 {
     /**
      * @var int
      */
-    private $maxAttempts;
+    private $lastAttempt;
     /**
      * @var int
      */
-    private $lastAttempt;
+    private $maxAttempts;
 
-    public function __construct(int $maxAttempts, int $lastAttempt = 0)
+    public function __construct(int $maxAttempts)
     {
+        $this->lastAttempt = 0;
         $this->maxAttempts = $maxAttempts;
-        $this->lastAttempt = $lastAttempt;
     }
 
     /**
diff --git a/tests/Retry/ExceptionClassifier/ExceptionClassifierTest.php b/tests/Retry/ExceptionClassifier/ExceptionClassifierTest.php
index 6798b45..635ce5a 100644
--- a/tests/Retry/ExceptionClassifier/ExceptionClassifierTest.php
+++ b/tests/Retry/ExceptionClassifier/ExceptionClassifierTest.php
@@ -7,23 +7,31 @@
 
 class ExceptionClassifierTest extends TestCase
 {
-    public function testDefaults(): void
+    public function testDefault(): void
     {
-        $classifier = new ExceptionClassifier();
+        $exceptionClassifier = new ExceptionClassifier();
 
-        $this->assertTrue($classifier->classify(new \Error()));
-        $this->assertTrue($classifier->classify(new \Exception()));
+        $this->assertTrue($exceptionClassifier->classify(new \Error()));
+        $this->assertTrue($exceptionClassifier->classify(new \Exception()));
     }
 
-    public function testClassify(): void
+    public function testInherited(): void
     {
-        $classifier = new ExceptionClassifier([
+        $exceptionClassifier = new ExceptionClassifier([
             \RuntimeException::class,
         ]);
 
-        $this->assertTrue($classifier->classify(new \RuntimeException()));
-        $this->assertTrue($classifier->classify(new \UnexpectedValueException()));
-        $this->assertFalse($classifier->classify(new \InvalidArgumentException()));
-        $this->assertFalse($classifier->classify(new \Exception()));
+        $this->assertTrue($exceptionClassifier->classify(new \RuntimeException()));
+        $this->assertTrue($exceptionClassifier->classify(new \UnexpectedValueException()));
+    }
+
+    public function testUnsupported(): void
+    {
+        $exceptionClassifier = new ExceptionClassifier([
+            \RuntimeException::class,
+        ]);
+
+        $this->assertFalse($exceptionClassifier->classify(new \InvalidArgumentException()));
+        $this->assertFalse($exceptionClassifier->classify(new \Exception()));
     }
 }
diff --git a/tests/Retry/RetryTest.php b/tests/Retry/RetryTest.php
index 4bd221d..4913af3 100644
--- a/tests/Retry/RetryTest.php
+++ b/tests/Retry/RetryTest.php
@@ -31,11 +31,11 @@ public function testThrowException(): void
     {
         $backOff = new ConstantBackOff(0, 0);
 
-        $classifier = new ExceptionClassifier([
+        $exceptionClassifier = new ExceptionClassifier([
             \RuntimeException::class,
         ]);
 
-        $retry = new Retry($backOff, $classifier);
+        $retry = new Retry($backOff, $exceptionClassifier);
 
         $this->expectException(\RuntimeException::class);
 
@@ -46,20 +46,20 @@ public function testThrowException(): void
 
     public function testAttemptsCounter(): void
     {
-        $counter = new BackOffCounter(3);
+        $attemptsCounter = new AttemptsCounter(3);
 
-        $classifier = new ExceptionClassifier([
+        $exceptionClassifier = new ExceptionClassifier([
             \RuntimeException::class,
         ]);
 
-        $retry = new Retry($counter, $classifier);
+        $retry = new Retry($attemptsCounter, $exceptionClassifier);
 
         try {
             $retry->call(function () {
                 throw new \RuntimeException();
             });
         } catch (\RuntimeException $e) {
-            $this->assertSame(3, $counter->getLastAttempt());
+            $this->assertSame(3, $attemptsCounter->getLastAttempt());
         }
     }
 }
diff --git a/tests/Strategy/ConstantStrategyTest.php b/tests/Strategy/ConstantStrategyTest.php
index c6757c9..9e7300e 100644
--- a/tests/Strategy/ConstantStrategyTest.php
+++ b/tests/Strategy/ConstantStrategyTest.php
@@ -10,9 +10,9 @@ class ConstantStrategyTest extends TestCase
 {
     public function testCalculate(): void
     {
-        $strategy = new ConstantStrategy();
+        $constantStrategy = new ConstantStrategy();
 
-        $duration = $strategy->calculate(new Milliseconds(1000), 3);
+        $duration = $constantStrategy->calculate(new Milliseconds(1000), 3);
 
         $this->assertEquals(1000, $duration->asMilliseconds());
     }
diff --git a/tests/Strategy/DecorrelationJitterStrategyTest.php b/tests/Strategy/DecorrelationJitterStrategyTest.php
index b589424..19c55dc 100644
--- a/tests/Strategy/DecorrelationJitterStrategyTest.php
+++ b/tests/Strategy/DecorrelationJitterStrategyTest.php
@@ -10,9 +10,9 @@ class DecorrelationJitterStrategyTest extends TestCase
 {
     public function testCalculate(): void
     {
-        $strategy = new DecorrelationJitterStrategy(3);
+        $decorrelationJitterStrategy = new DecorrelationJitterStrategy(3);
 
-        $duration = $strategy->calculate(new Milliseconds(1000), 0);
+        $duration = $decorrelationJitterStrategy->calculate(new Milliseconds(1000), 0);
 
         $this->assertGreaterThanOrEqual(1000, $duration->asMilliseconds());
         $this->assertLessThanOrEqual(3000, $duration->asMilliseconds());
diff --git a/tests/Strategy/ExponentialStrategyTest.php b/tests/Strategy/ExponentialStrategyTest.php
index 0874242..f29b090 100644
--- a/tests/Strategy/ExponentialStrategyTest.php
+++ b/tests/Strategy/ExponentialStrategyTest.php
@@ -10,9 +10,9 @@ class ExponentialStrategyTest extends TestCase
 {
     public function testCalculate(): void
     {
-        $strategy = new ExponentialStrategy(2);
+        $exponentialStrategy = new ExponentialStrategy(2);
 
-        $duration = $strategy->calculate(new Milliseconds(1000), 3);
+        $duration = $exponentialStrategy->calculate(new Milliseconds(1000), 3);
 
         $this->assertEquals(8000, $duration->asMilliseconds());
     }
diff --git a/tests/Strategy/LinearStrategyTest.php b/tests/Strategy/LinearStrategyTest.php
index f97ec32..5de8408 100644
--- a/tests/Strategy/LinearStrategyTest.php
+++ b/tests/Strategy/LinearStrategyTest.php
@@ -10,9 +10,9 @@ class LinearStrategyTest extends TestCase
 {
     public function testCalculate(): void
     {
-        $strategy = new LinearStrategy();
+        $linearStrategy = new LinearStrategy();
 
-        $duration = $strategy->calculate(new Milliseconds(1000), 3);
+        $duration = $linearStrategy->calculate(new Milliseconds(1000), 3);
 
         $this->assertEquals(4000, $duration->asMilliseconds());
     }