Adding unit tests for DateTimeType + minor fix

Author: moufmouf

src/Types/DateTimeType.php

@@ -6,10 +6,10 @@
 
 use DateTime;
 use DateTimeImmutable;
+use Exception;
 use GraphQL\Error\InvariantViolation;
 use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\StringValueNode;
-use GraphQL\Language\AST\ValueNode;
 use GraphQL\Type\Definition\ScalarType;
 use GraphQL\Utils\Utils;
 
@@ -75,6 +75,7 @@ public function parseLiteral($valueNode, array $variables = null)
             return $valueNode->value;
         }
 
-        return null;
+        // Intentionally without message, as all information already in wrapped Exception
+        throw new Exception();
     }
 }

tests/Types/DateTimeTypeTest.php

@@ -0,0 +1,42 @@
+<?php
+
+namespace TheCodingMachine\GraphQLite\Types;
+
+use DateTimeImmutable;
+use Exception;
+use GraphQL\Error\InvariantViolation;
+use GraphQL\Language\AST\StringValueNode;
+use PHPUnit\Framework\TestCase;
+
+class DateTimeTypeTest extends TestCase
+{
+
+    public function testSerialize(): void
+    {
+        $dateTimeType = DateTimeType::getInstance();
+
+        $this->assertSame('2019-05-05T10:10:10+00:00', $dateTimeType->serialize(new DateTimeImmutable('2019-05-05T10:10:10+00:00')));
+
+        $this->expectException(InvariantViolation::class);
+        $dateTimeType->serialize('foo');
+    }
+
+    public function testParseLiteral(): void
+    {
+        $dateTimeType = DateTimeType::getInstance();
+
+        $this->assertSame('2019-05-05T10:10:10+00:00', $dateTimeType->parseLiteral(new StringValueNode(['value' => '2019-05-05T10:10:10+00:00'])));
+
+        $this->expectException(Exception::class);
+        $dateTimeType->parseLiteral(null);
+
+    }
+
+    public function testParseValue(): void
+    {
+        $dateTimeType = DateTimeType::getInstance();
+
+
+        $this->assertNull($dateTimeType->parseValue(null));
+    }
+}