Tests/reorganize: move encodeString tests to own file

Note: this doesn't move the complete test from the original test file, just select parts of the test method.

test/PHPMailer/EncodeStringTest.php

@@ -0,0 +1,43 @@
+<?php
+
+/**
+ * PHPMailer - PHP email transport unit tests.
+ * PHP version 5.5.
+ *
+ * @author    Marcus Bointon <phpmailer@synchromedia.co.uk>
+ * @author    Andy Prevost
+ * @copyright 2012 - 2020 Marcus Bointon
+ * @copyright 2004 - 2009 Andy Prevost
+ * @license   http://www.gnu.org/copyleft/lesser.html GNU Lesser General Public License
+ */
+
+namespace PHPMailer\Test\PHPMailer;
+
+use PHPMailer\PHPMailer\PHPMailer;
+use PHPMailer\Test\TestCase;
+
+/**
+ * Test string encoding functionality.
+ */
+final class EncodeStringTest extends TestCase
+{
+
+    /**
+     * Encoding and charset tests.
+     */
+    public function testEncodings()
+    {
+        self::assertSame(
+            'hello',
+            $this->Mail->encodeString('hello', 'binary'),
+            'Binary encoding changed input'
+        );
+        $this->Mail->ErrorInfo = '';
+        $this->Mail->encodeString('hello', 'asdfghjkl');
+        self::assertNotEmpty($this->Mail->ErrorInfo, 'Invalid encoding not detected');
+        self::assertMatchesRegularExpression(
+            '/' . base64_encode('hello') . '/',
+            $this->Mail->encodeString('hello')
+        );
+    }
+}

test/PHPMailer/PHPMailerTest.php

@@ -894,19 +894,6 @@ EOT;
             $this->Mail->encodeQ("Nov\xc3\xa1=", 'text'),
             'Q Encoding (text) failed 2'
         );
-
-        self::assertSame(
-            'hello',
-            $this->Mail->encodeString('hello', 'binary'),
-            'Binary encoding changed input'
-        );
-        $this->Mail->ErrorInfo = '';
-        $this->Mail->encodeString('hello', 'asdfghjkl');
-        self::assertNotEmpty($this->Mail->ErrorInfo, 'Invalid encoding not detected');
-        self::assertMatchesRegularExpression(
-            '/' . base64_encode('hello') . '/',
-            $this->Mail->encodeString('hello')
-        );
     }
 
     /**