MDL-65919 core: add test for table download

lib/tests/tablelib_test.php

@@ -618,4 +618,26 @@ class core_tablelib_testcase extends basic_testcase {
         unset($_GET['tifirst']);
         $this->assertTrue($table->can_be_reset());
     }
+
+    /**
+     * Test export in CSV format
+     */
+    public function test_table_export() {
+        $table = new flexible_table('tablelib_test_export');
+        $table->define_baseurl('/invalid.php');
+        $table->define_columns(['c1', 'c2', 'c3']);
+        $table->define_headers(['Col1', 'Col2', 'Col3']);
+
+        ob_start();
+        $table->is_downloadable(true);
+        $table->is_downloading('csv');
+
+        $table->setup();
+        $table->add_data(['column0' => 'a', 'column1' => 'b', 'column2' => 'c']);
+        $output = ob_get_contents();
+        ob_end_clean();
+
+        $this->assertEquals("Col1,Col2,Col3\na,b,c\n", substr($output, 3));
+    }
+
 }