Make sure transformers match API definition.

tests/Unit/Transformers/CurrencyExchangeRateTransformerTest.php

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+<?php
+/**
+ * CurrencyExchangeRateTransformerTest.php
+ * Copyright (c) 2018 thegrumpydictator@gmail.com
+ *
+ * This file is part of Firefly III.
+ *
+ * Firefly III is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Firefly III is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Firefly III. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+declare(strict_types=1);
+
+namespace Tests\Unit\Transformers;
+
+
+use Carbon\Carbon;
+use FireflyIII\Models\CurrencyExchangeRate;
+use FireflyIII\Models\TransactionCurrency;
+use FireflyIII\Transformers\CurrencyExchangeRateTransformer;
+use Log;
+use Symfony\Component\HttpFoundation\ParameterBag;
+use Tests\TestCase;
+
+/**
+ *
+ * Class CurrencyExchangeRateTransformerTest
+ */
+class CurrencyExchangeRateTransformerTest extends TestCase
+{
+    /**
+     *
+     */
+    public function setUp(): void
+    {
+        parent::setUp();
+        Log::info(sprintf('Now in %s.', \get_class($this)));
+    }
+
+    /**
+     * @covers \FireflyIII\Transformers\CurrencyExchangeRateTransformer
+     */
+    public function testBasic()
+    {
+        $date                  = new Carbon;
+        $eur                   = TransactionCurrency::whereCode('EUR')->first();
+        $usd                   = TransactionCurrency::whereCode('USD')->first();
+        $cer                   = new CurrencyExchangeRate;
+        $cer->from_currency_id = $eur->id;
+        $cer->to_currency_id   = $usd->id;
+        $cer->created_at       = new Carbon;
+        $cer->updated_at       = new Carbon;
+        $cer->rate             = 1.5;
+        $cer->date             = $date;
+
+        $parameters = new ParameterBag;
+        $parameters->set('amount', '100');
+
+        $transformer = app(CurrencyExchangeRateTransformer::class);
+        $transformer->setParameters($parameters);
+        $result = $transformer->transform($cer);
+
+        $this->assertEquals($cer->from_currency_id, $result['from_currency_id']);
+        $this->assertEquals(150, $result['amount']);
+
+
+    }
+}