Fix: phpunit include tests path (#230)

* Fix phpunit include path

* Add tests for Covariance

phpunit.xml

@@ -9,7 +9,7 @@
         enforceTimeLimit="true"
 >
     <testsuite name="PHP-ML Test Suite">
-        <directory>tests/*</directory>
+        <directory>tests</directory>
     </testsuite>
 
     <filter>

src/Math/Statistic/Covariance.php

@@ -4,7 +4,6 @@ declare(strict_types=1);
 
 namespace Phpml\Math\Statistic;
 
-use Exception;
 use Phpml\Exception\InvalidArgumentException;
 
 class Covariance
@@ -64,7 +63,7 @@ class Covariance
         }
 
         if ($i < 0 || $k < 0 || $i >= $n || $k >= $n) {
-            throw new Exception('Given indices i and k do not match with the dimensionality of data');
+            throw new InvalidArgumentException('Given indices i and k do not match with the dimensionality of data');
         }
 
         if ($meanX === null || $meanY === null) {

tests/Math/Statistic/CovarianceTest.php

@@ -4,6 +4,7 @@ declare(strict_types=1);
 
 namespace Phpml\Tests\Math\Statistic;
 
+use Phpml\Exception\InvalidArgumentException;
 use Phpml\Math\Statistic\Covariance;
 use Phpml\Math\Statistic\Mean;
 use PHPUnit\Framework\TestCase;
@@ -59,4 +60,46 @@ class CovarianceTest extends TestCase
         $covariance = Covariance::covarianceMatrix($matrix, [$meanX, $meanY]);
         $this->assertEquals($knownCovariance, $covariance, '', $epsilon);
     }
+
+    public function testThrowExceptionOnEmptyX(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        Covariance::fromXYArrays([], [1, 2, 3]);
+    }
+
+    public function testThrowExceptionOnEmptyY(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        Covariance::fromXYArrays([1, 2, 3], []);
+    }
+
+    public function testThrowExceptionOnToSmallArrayIfSample(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        Covariance::fromXYArrays([1], [2], true);
+    }
+
+    public function testThrowExceptionIfEmptyDataset(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        Covariance::fromDataset([], 0, 1);
+    }
+
+    public function testThrowExceptionOnToSmallDatasetIfSample(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        Covariance::fromDataset([1], 0, 1);
+    }
+
+    public function testThrowExceptionWhenKIndexIsOutOfBound(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        Covariance::fromDataset([1, 2, 3], 2, 5);
+    }
+
+    public function testThrowExceptionWhenIIndexIsOutOfBound(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        Covariance::fromDataset([1, 2, 3], 5, 2);
+    }
 }