Add a trait that checks to see if $this->exporter()->export() is avai…

…lable before trying to use it

src/Constraints/ContainsSelector.php

@@ -11,6 +11,8 @@
  */
 class ContainsSelector extends Constraint
 {
+    use ExporterTrait;
+
     /**
      * @var Selector
      */
@@ -31,7 +33,7 @@ public function __construct(Selector $selector)
      */
     public function toString(): string
     {
-        return 'contains selector ' . $this->exporter()->export($this->selector->getValue());
+        return 'contains selector ' . $this->exportValue($this->selector->getValue());
     }
 
     /**

src/Constraints/ElementContainsString.php

@@ -11,6 +11,8 @@
  */
 class ElementContainsString extends Constraint
 {
+    use ExporterTrait;
+
     /**
      * A cache of matches that we have checked against.
      *
@@ -56,7 +58,7 @@ public function toString(): string
         return sprintf(
             '%s string %s',
             count($this->matchingElements) >= 2 ? 'contain' : 'contains',
-            $this->exporter()->export($this->needle)
+            $this->exportValue($this->needle)
         );
     }
 
@@ -115,7 +117,7 @@ protected function failureDescription($html): string
 
         return sprintf(
             $label,
-            $this->exporter()->export($this->selector->getValue()),
+            $this->exportValue($this->selector->getValue()),
             $this->toString()
         );
     }

src/Constraints/ElementMatchesRegExp.php

@@ -12,6 +12,8 @@
  */
 class ElementMatchesRegExp extends ElementContainsString
 {
+    use ExporterTrait;
+
     /**
      * @var string
      */
@@ -37,7 +39,7 @@ public function toString(): string
         return sprintf(
             '%s regular expression %s',
             count($this->matchingElements) >= 2 ? 'match' : 'matches',
-            $this->exporter()->export($this->pattern)
+            $this->exportValue($this->pattern)
         );
     }
 

src/Constraints/ExporterTrait.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace SteveGrunwell\PHPUnit_Markup_Assertions\Constraints;
+
+/**
+ * Trait that exposes an exportValue method that will attempt to use
+ * {@see SebastianBergmann\Exporter\Exporter} when available.
+ */
+trait ExporterTrait
+{
+    /**
+     * Export a value to include it in error messages.
+     *
+     * If {@see SebastianBergmann\Exporter\Exporter} is available (as it is in modern versions of
+     * PHPUnit), then it will be used. Otherwise, we'll do a simple var_export().
+     *
+     * @param mixed $value The value to be exported.
+     *
+     * @return string A string representation of the value.
+     */
+    private function exportValue($value): string
+    {
+        if (method_exists($this, 'exporter')) {
+            return $this->exporter()->export($value);
+        }
+
+        return var_export($value, true);
+    }
+}

src/Constraints/SelectorCount.php

@@ -11,6 +11,8 @@
  */
 class SelectorCount extends Constraint
 {
+    use ExporterTrait;
+
     /**
      * @var int
      */
@@ -41,7 +43,7 @@ public function toString(): string
         return sprintf(
             'contains %d instance(s) of selector %s',
             $this->count,
-            $this->exporter()->export($this->selector->getValue())
+            $this->exportValue($this->selector->getValue())
         );
     }