Added the test to validate test environment itself

We should make sure that the environment the tests are run is as strict
as possible. For example, zend.assertions should be enabled.

tests/TestEnvironmentTest.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace Psalm\Tests;
+
+use PHPUnit\Framework\TestCase as PHPUnitTestCase;
+
+use function ini_get;
+
+class TestEnvironmentTest extends PHPUnitTestCase
+{
+    public function testIniSettings(): void
+    {
+        $this->assertSame(
+            '1',
+            ini_get('zend.assertions'),
+            'zend.assertions should be set to 1 to increase test strictness',
+        );
+    }
+}