Currency should be JSON serializable (#79)

src/AbstractMoney.php

@@ -226,7 +226,7 @@ final public function jsonSerialize(): array
     {
         return [
             'amount' => (string) $this->getAmount(),
-            'currency' => (string) $this->getCurrency()
+            'currency' => $this->getCurrency()->jsonSerialize()
         ];
     }
 }

src/Currency.php

@@ -5,12 +5,13 @@
 namespace Brick\Money;
 
 use Brick\Money\Exception\UnknownCurrencyException;
+use JsonSerializable;
 use Stringable;
 
 /**
  * A currency. This class is immutable.
  */
-final class Currency implements Stringable
+final class Currency implements Stringable, JsonSerializable
 {
     /**
      * The currency code.
@@ -166,6 +167,11 @@ public function is(Currency|string|int $currency) : bool
             || ($this->numericCode !== 0 && $this->numericCode === (int) $currency);
     }
 
+    final public function jsonSerialize(): string
+    {
+        return $this->currencyCode;
+    }
+
     /**
      * Returns the currency code.
      */

tests/CurrencyTest.php

@@ -123,4 +123,20 @@ public function testIs() : void
         self::assertNotSame($currency, $clone);
         self::assertTrue($clone->is($currency));
     }
+
+    /**
+     * @dataProvider providerJsonSerialize
+     */
+    public function testJsonSerialize(Currency $currency, string $expected): void
+    {
+        self::assertSame($expected, $currency->jsonSerialize());
+        self::assertSame(json_encode($expected), json_encode($currency));
+    }
+
+    public function providerJsonSerialize(): array
+    {
+        return [
+            [Currency::of('USD'), 'USD']
+        ];
+    }
 }