Update TestCase class references.

Author: mcordingley

tests/Decomposition/LUPTest.php

@@ -7,9 +7,9 @@
 use MCordingley\LinearAlgebra\Decomposition\LUP;
 use MCordingley\LinearAlgebra\Matrix;
 use MCordingley\LinearAlgebra\MatrixException;
-use PHPUnit_Framework_TestCase;
+use PHPUnit\Framework\TestCase;
 
-final class LUPTest extends PHPUnit_Framework_TestCase
+final class LUPTest extends TestCase
 {
     public function testNonSquare()
     {

tests/Decomposition/LUTest.php

@@ -7,9 +7,9 @@
 use MCordingley\LinearAlgebra\Decomposition\LU;
 use MCordingley\LinearAlgebra\Matrix;
 use MCordingley\LinearAlgebra\MatrixException;
-use PHPUnit_Framework_TestCase;
+use PHPUnit\Framework\TestCase;
 
-final class LUTest extends PHPUnit_Framework_TestCase
+final class LUTest extends TestCase
 {
     public function testNonSquare()
     {

tests/MatrixTest.php

@@ -7,9 +7,9 @@
 use MCordingley\LinearAlgebra\Matrix;
 use MCordingley\LinearAlgebra\MatrixException;
 use MCordingley\LinearAlgebra\Vector;
-use PHPUnit_Framework_TestCase;
+use PHPUnit\Framework\TestCase;
 
-final class MatrixTest extends PHPUnit_Framework_TestCase
+final class MatrixTest extends TestCase
 {
     private function buildMatrix()
     {

tests/VectorTest.php

@@ -7,8 +7,9 @@
 use MCordingley\LinearAlgebra\Matrix;
 use MCordingley\LinearAlgebra\MatrixException;
 use MCordingley\LinearAlgebra\Vector;
+use PHPUnit\Framework\TestCase;
 
-class VectorTest extends \PHPUnit_Framework_TestCase
+class VectorTest extends TestCase
 {
     private function buildVector()
     {