Encoding::__toString complies with PHP specification from now on

src/Smalot/PdfParser/Encoding.php

@@ -126,13 +126,23 @@ public function translateChar($dec)
     }
 
     /**
-     * @return string
+     * Returns the name of the encoding class, if available.
      *
-     * @throws \Exception
+     * @return string Returns encoding class name if available or empty string (only prior PHP 7.4).
+     *
+     * @throws \Exception On PHP 7.4+ an exception is thrown if encoding class doesn't exist.
      */
     public function __toString()
     {
-        return $this->getEncodingClass();
+        try {
+            return $this->getEncodingClass();
+        } catch (Exception $e) {
+            // prior to PHP 7.4 toString has to return an empty string.
+            if (version_compare(\PHP_VERSION, '7.4.0', '<')) {
+                return '';
+            }
+            throw $e;
+        }
     }
 
     /**

tests/Integration/EncodingTest.php

@@ -54,8 +54,13 @@ public function testGetEncodingClass()
 
     /**
      * This tests checks behavior if given Encoding class doesn't exist.
+     *
+     * Protected method getEncodingClass is called in init and __toString.
+     * It throws an exception if class is not available.
+     * Calling init is enough to trigger the exception, but __toString call afterwards
+     * makes sure that we don't missing it.
      */
-    public function testGetEncodingClassMissingClassException()
+    public function testInitGetEncodingClassMissingClassException()
     {
         $this->expectException(Exception::class);
         $this->expectExceptionMessage('Missing encoding data for: "invalid"');
@@ -67,4 +72,32 @@ public function testGetEncodingClassMissingClassException()
 
         $encoding->__toString();
     }
+
+    /**
+     * This tests focuses on behavior of Encoding::__toString when running PHP 7.4+ and prior.
+     *
+     * Prior PHP 7.4 we expect an empty string to be returned (based on PHP specification).
+     * PHP 7.4+ we expect an exception to be thrown when class is invalid.
+     */
+    public function testToStringGetEncodingClassMissingClassException()
+    {
+        // prior to PHP 7.4 toString has to return an empty string.
+        if (version_compare(\PHP_VERSION, '7.4.0', '<')) {
+            $header = new Header(['BaseEncoding' => new Element('invalid')]);
+
+            $encoding = new Encoding(new Document(), $header);
+
+            $this->assertEquals('', $encoding->__toString());
+        } else {
+            // PHP 7.4+
+            $this->expectException(Exception::class);
+            $this->expectExceptionMessage('Missing encoding data for: "invalid"');
+
+            $header = new Header(['BaseEncoding' => new Element('invalid')]);
+
+            $encoding = new Encoding(new Document(), $header);
+
+            $encoding->__toString();
+        }
+    }
 }