Add return typehints to toString methods for compatibility with PHPUnit 7

Author: emodric

PhpUnit/ConfigurationValuesAreInvalidConstraint.php

@@ -41,7 +41,7 @@ public function evaluate($other, $description = '', $returnResult = false)
         $this->fail($other, $description);
     }
 
-    public function toString()
+    public function toString(): string
     {
         $toString = 'is invalid for the given configuration';
 

PhpUnit/ConfigurationValuesAreValidConstraint.php

@@ -34,7 +34,7 @@ public function evaluate($other, $description = '', $returnResult = false)
         }
     }
 
-    public function toString()
+    public function toString(): string
     {
         return 'is valid for the given configuration';
     }

PhpUnit/ProcessedConfigurationEqualsConstraint.php

@@ -29,8 +29,9 @@ public function evaluate($other, $description = '', $returnResult = false)
         return $constraint->evaluate($processedConfiguration, '', $returnResult);
     }
 
-    public function toString()
+    public function toString(): string
     {
         // won't be used, this constraint only wraps IsEqual
+        return '';
     }
 }

Tests/PhpUnit/ProcessedConfigurationEqualsConstraintTest.php

@@ -47,6 +47,6 @@ public function to_string_is_not_implemented()
             array()
         );
 
-        $this->assertNull($constraint->toString());
+        $this->assertEquals('', $constraint->toString());
     }
 }