Add CSV download trait

.gitignore

@@ -0,0 +1 @@
+.idea

README.md

@@ -97,3 +97,26 @@ E.g
    '/node/add/.*',
  ];
 ```
+
+## CsvDownloadTrait
+
+A trait to interact with Views CSV exports making it easy to make assertions on CSV output.
+
+This trait requires the `league/csv` library which is included in the views_data_export module (via csv_serialization).
+
+### Usage
+
+Once your trait is added to your test base class, you can get CSV output into a variable and then make assertions on the contents.
+
+```php
+$this->drupalGet('admin/content');
+// Pass TRUE if your CSV is batched, otherwise FALSE.
+$csv = $this->assertViewsCsvExportRowCount(3, TRUE);
+$csv->next();
+$row = $csv->current();
+$this->assertEquals([
+  'Title' => 'Foo bar',
+  'Content type' => 'Basic',
+  'Status' => 'Published',
+], $row);
+```

src/Traits/CsvDownloadTrait.php

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+<?php
+
+declare(strict_types=1);
+
+namespace PNX\DrupalTestUtils\Traits;
+
+use League\Csv\CharsetConverter;
+use League\Csv\Reader;
+
+/**
+ * CSV download trait.
+ */
+trait CsvDownloadTrait {
+
+  /**
+   * Asserts that a CSV export has a certain number of rows.
+   *
+   * Clicks the orange 'CSV' button displayed in views, waits for batch to run,
+   * then asserts contents of download.
+   */
+  protected function assertViewsCsvExportRowCount(int $count, bool $isBatch = TRUE, string $csvLinkText = 'Download CSV'): Reader {
+    $this->clickLink($csvLinkText);
+    $csvReader = $this->waitForCsv($isBatch);
+    $this->assertCount($count, $csvReader->getRecords());
+    return $csvReader;
+  }
+
+  /**
+   * Wait for a CSV to finish (batch or standard) and return a Reader.
+   */
+  protected function waitForCsv(bool $isBatch = TRUE): Reader {
+    if ($isBatch) {
+      $this->checkForMetaRefresh();
+      $this->assertSession()->pageTextContains('Export complete. Download the file here.');
+      $this->clickLink('here');
+    }
+    $csv = $this->getSession()
+      ->getDriver()
+      ->getContent();
+    $csvReader = Reader::createFromString($csv);
+    if ($csvReader->getInputBOM() === Reader::BOM_UTF16_LE) {
+      CharsetConverter::addTo($csvReader, 'UTF-16', 'UTF-8');
+    }
+    $csvReader->setHeaderOffset(0);
+    return $csvReader;
+  }
+
+}