Add database test for import model

Refs #2446

tests/fixtures/backend/reference/file1.txt

@@ -0,0 +1 @@
+File one contents

tests/fixtures/backend/reference/file2.txt

@@ -0,0 +1 @@
+FILE TWO CONTENTS

tests/unit/plugins/backend/ImportModelDbTest.php

@@ -0,0 +1,40 @@
+<?php
+
+use Backend\Models\ImportModel;
+use System\Models\File as FileModel;
+
+class ExampleDbImportModel extends ImportModel
+{
+    public $rules = [];
+
+    public function importData($results, $sessionKey = null)
+    {
+        return [];
+    }
+}
+
+class ImportModelDbTest extends PluginTestCase
+{
+    public function testGetImportFilePath()
+    {
+        $model = new ExampleDbImportModel;
+        $sessionKey = uniqid('session_key', true);
+
+        $file1 = FileModel::create([
+            'data' => base_path().'/tests/fixtures/backend/reference/file1.txt'
+        ]);
+
+        $file2 = FileModel::create([
+            'data' => base_path().'/tests/fixtures/backend/reference/file2.txt'
+        ]);
+
+        $model->import_file()->add($file1, $sessionKey);
+        $model->import_file()->add($file2, $sessionKey);
+
+        $this->assertEquals(
+            $file2->getLocalPath(),
+            $model->getImportFilePath($sessionKey),
+            'ImportModel::getImportFilePath() should return the last uploaded file.'
+        );
+    }
+}