diff --git a/src/Chunk.php b/src/Chunk.php
index 317ed867..49c77575 100644
--- a/src/Chunk.php
+++ b/src/Chunk.php
@@ -33,7 +33,7 @@ final class Chunk
     private $endRange;
 
     /**
-     * @var array
+     * @var Line[]
      */
     private $lines;
 
@@ -66,13 +66,25 @@ public function getEndRange()
         return $this->endRange;
     }
 
+    /**
+     * @return Line[]
+     */
     public function getLines()
     {
         return $this->lines;
     }
 
+    /**
+     * @param Line[] $lines
+     */
     public function setLines(array $lines)
     {
+        foreach ($lines as $line) {
+            if (!$line instanceof Line) {
+                throw new InvalidArgumentException;
+            }
+        }
+
         $this->lines = $lines;
     }
 }
diff --git a/tests/ChunkTest.php b/tests/ChunkTest.php
index 29fec466..cf038cd0 100644
--- a/tests/ChunkTest.php
+++ b/tests/ChunkTest.php
@@ -14,6 +14,8 @@
 
 /**
  * @covers PhpCsFixer\Diff\Chunk
+ *
+ * @uses PhpCsFixer\Diff\Line
  */
 final class ChunkTest extends TestCase
 {
@@ -27,6 +29,11 @@ protected function setUp()
         $this->chunk = new Chunk;
     }
 
+    public function testHasInitiallyNoLines()
+    {
+        $this->assertSame([], $this->chunk->getLines());
+    }
+
     public function testCanBeCreatedWithoutArguments()
     {
         $this->assertInstanceOf(Chunk::class, $this->chunk);
@@ -59,10 +66,10 @@ public function testLinesCanBeRetrieved()
 
     public function testLinesCanBeSet()
     {
-        $this->assertSame([], $this->chunk->getLines());
+        $lines = [new Line(Line::ADDED, 'added'), new Line(Line::REMOVED, 'removed')];
+
+        $this->chunk->setLines($lines);
 
-        $testValue = ['line0', 'line1'];
-        $this->chunk->setLines($testValue);
-        $this->assertSame($testValue, $this->chunk->getLines());
+        $this->assertSame($lines, $this->chunk->getLines());
     }
 }
diff --git a/tests/LongestCommonSubsequenceTest.php b/tests/LongestCommonSubsequenceTest.php
index 47856642..c49a58f1 100644
--- a/tests/LongestCommonSubsequenceTest.php
+++ b/tests/LongestCommonSubsequenceTest.php
@@ -35,7 +35,7 @@ abstract class LongestCommonSubsequenceTest extends TestCase
     protected function setUp()
     {
         $this->memoryLimit = \ini_get('memory_limit');
-        \ini_set('memory_limit', '256M');
+        \ini_set('memory_limit', '-1');
 
         $this->implementation = $this->createImplementation();
     }
diff --git a/tests/Output/Integration/StrictUnifiedDiffOutputBuilderIntegrationTest.php b/tests/Output/Integration/StrictUnifiedDiffOutputBuilderIntegrationTest.php
index 1c28f941..f39d8fea 100644
--- a/tests/Output/Integration/StrictUnifiedDiffOutputBuilderIntegrationTest.php
+++ b/tests/Output/Integration/StrictUnifiedDiffOutputBuilderIntegrationTest.php
@@ -21,6 +21,7 @@
  *
  * @uses PhpCsFixer\Diff\Differ
  * @uses PhpCsFixer\Diff\TimeEfficientLongestCommonSubsequenceCalculator
+ * @uses PhpCsFixer\Diff\MemoryEfficientLongestCommonSubsequenceCalculator
  *
  * @requires OS Linux
  */
diff --git a/tests/Output/StrictUnifiedDiffOutputBuilderTest.php b/tests/Output/StrictUnifiedDiffOutputBuilderTest.php
index 0123d9a4..2c770c58 100644
--- a/tests/Output/StrictUnifiedDiffOutputBuilderTest.php
+++ b/tests/Output/StrictUnifiedDiffOutputBuilderTest.php
@@ -19,6 +19,8 @@
  * @covers PhpCsFixer\Diff\Output\StrictUnifiedDiffOutputBuilder
  *
  * @uses PhpCsFixer\Diff\Differ
+ * @uses PhpCsFixer\Diff\TimeEfficientLongestCommonSubsequenceCalculator
+ * @uses PhpCsFixer\Diff\ConfigurationException
  */
 final class StrictUnifiedDiffOutputBuilderTest extends TestCase
 {
diff --git a/tests/ParserTest.php b/tests/ParserTest.php
index 207e23d3..1bbe5968 100644
--- a/tests/ParserTest.php
+++ b/tests/ParserTest.php
@@ -38,12 +38,10 @@ public function testParse()
 
         $diffs = $this->parser->parse($content);
 
-        $this->assertInternalType('array', $diffs);
         $this->assertContainsOnlyInstancesOf(Diff::class, $diffs);
         $this->assertCount(1, $diffs);
 
         $chunks = $diffs[0]->getChunks();
-        $this->assertInternalType('array', $chunks);
         $this->assertContainsOnlyInstancesOf(Chunk::class, $chunks);
 
         $this->assertCount(1, $chunks);
@@ -75,7 +73,7 @@ public function testParseWithMultipleChunks()
 
     public function testParseWithRemovedLines()
     {
-        $content = <<<A
+        $content = <<<END
 diff --git a/Test.txt b/Test.txt
 index abcdefg..abcdefh 100644
 --- a/Test.txt
@@ -83,15 +81,13 @@ public function testParseWithRemovedLines()
 @@ -49,9 +49,8 @@
  A
 -B
-A;
+END;
         $diffs = $this->parser->parse($content);
-        $this->assertInternalType('array', $diffs);
         $this->assertContainsOnlyInstancesOf(Diff::class, $diffs);
         $this->assertCount(1, $diffs);
 
         $chunks = $diffs[0]->getChunks();
 
-        $this->assertInternalType('array', $chunks);
         $this->assertContainsOnlyInstancesOf(Chunk::class, $chunks);
         $this->assertCount(1, $chunks);
 
@@ -102,7 +98,6 @@ public function testParseWithRemovedLines()
         $this->assertSame(8, $chunk->getEndRange());
 
         $lines = $chunk->getLines();
-        $this->assertInternalType('array', $lines);
         $this->assertContainsOnlyInstancesOf(Line::class, $lines);
         $this->assertCount(2, $lines);
 
@@ -118,7 +113,7 @@ public function testParseWithRemovedLines()
 
     public function testParseDiffForMulitpleFiles()
     {
-        $content = <<<A
+        $content = <<<END
 diff --git a/Test.txt b/Test.txt
 index abcdefg..abcdefh 100644
 --- a/Test.txt
@@ -134,7 +129,7 @@ public function testParseDiffForMulitpleFiles()
 @@ -1,2 +1,3 @@
  A
 +B
-A;
+END;
         $diffs = $this->parser->parse($content);
         $this->assertCount(2, $diffs);
 
diff --git a/tests/Utils/UnifiedDiffAssertTrait.php b/tests/Utils/UnifiedDiffAssertTrait.php
index 56093e88..8598fe96 100644
--- a/tests/Utils/UnifiedDiffAssertTrait.php
+++ b/tests/Utils/UnifiedDiffAssertTrait.php
@@ -27,6 +27,7 @@ public function assertValidUnifiedDiffFormat($diff)
 
         // test diff ends with a line break
         $last = \substr($diff, -1);
+
         if ("\n" !== $last && "\r" !== $last) {
             throw new \UnexpectedValueException(\sprintf('Expected diff to end with a line break, got "%s".', $last));
         }
@@ -130,6 +131,7 @@ public function assertValidUnifiedDiffFormat($diff)
                 }
 
                 $previousType = $this->unifiedDiffAssertLinePrefix($lines[$lineNumber - 2], \sprintf('Preceding line of "\\ No newline at end of file" of unexpected format. Line %d.', $lineNumber));
+
                 if (isset($endOfLineTypes[$previousType])) {
                     throw new \UnexpectedValueException(\sprintf('Unexpected "\\ No newline at end of file", "%s" was already closed. Line %d.', $type, $lineNumber));
                 }
@@ -190,6 +192,7 @@ private function unifiedDiffAssertLinePrefix($line, $message)
     private function unifiedDiffAssertStrLength($line, $min, $message)
     {
         $length = \strlen($line);
+
         if ($length < $min) {
             throw new \UnexpectedValueException(\sprintf('Expected string length of minimal %d, got %d. %s', $min, $length, $message));
         }