Add test for PHP 7.1 nullable types

tests/Php71Test.php

@@ -0,0 +1,61 @@
+<?php
+namespace Psalm\Tests;
+
+use PhpParser\ParserFactory;
+use PHPUnit_Framework_TestCase;
+use Psalm\Checker\FileChecker;
+use Psalm\Config;
+use Psalm\Context;
+
+class Php71Test extends PHPUnit_Framework_TestCase
+{
+    protected static $parser;
+
+    public static function setUpBeforeClass()
+    {
+        self::$parser = (new ParserFactory)->create(ParserFactory::PREFER_PHP7);
+
+        $config = Config::getInstance();
+        $config->throw_exception = true;
+        $config->use_docblock_types = true;
+    }
+
+    public function setUp()
+    {
+        FileChecker::clearCache();
+    }
+
+    public function testNullableReturnType()
+    {
+        $stmts = self::$parser->parse('<?php
+        function a(): ?string
+        {
+            return rand(0, 10) ? "elePHPant" : null;
+        }
+
+        $a = a();
+        ');
+
+        $file_checker = new FileChecker('somefile.php', $stmts);
+        $context = new Context('somefile.php');
+        $file_checker->check(true, true, $context);
+        $this->assertEquals('string|null', (string) $context->vars_in_scope['$a']);
+    }
+
+    public function testNullableArgument()
+    {
+        $stmts = self::$parser->parse('<?php
+        function test(?string $name) : ?string
+        {
+            return $name;
+        }
+
+        test("elePHPant");
+        test(null);
+        ');
+
+        $file_checker = new FileChecker('somefile.php', $stmts);
+        $context = new Context('somefile.php');
+        $file_checker->check(true, true, $context);
+    }
+}