Index: core/modules/simpletest/simpletest.module
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- core/modules/simpletest/simpletest.module	(revision 74c8c59941c904f2e3de37e6550e66c4051dc3c0)
+++ core/modules/simpletest/simpletest.module	(revision )
@@ -489,6 +489,11 @@
 /**
  * Generates test file.
  *
+ * The file is prefixed by its type:
+ * - text-*.txt and text-* (no extension)
+ * - binary-* (no extension)
+ *
+ *
  * @param string $filename
  *   The name of the file, including the path.
  * @param int $width
Index: core/modules/simpletest/src/WebTestBase.php
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- core/modules/simpletest/src/WebTestBase.php	(revision 74c8c59941c904f2e3de37e6550e66c4051dc3c0)
+++ core/modules/simpletest/src/WebTestBase.php	(revision )
@@ -446,16 +446,42 @@
   }
 
   /**
-   * Gets a list files that can be used in tests.
+   * Returns files generated by the function simplest_generate_files()
+   * which is in simpletest.module. These files can then be used in tests.
    *
+   * The first time this method is called, the class will generate numerous
+   * test files in text and binary format. These files are stored in
+   * public:// and can be used for tests. It will copy all files in
+   * core/modules/simpletest/files to public:// as well. These contain image,
+   * SQL, PHP, JavaScript and HTML files, and they will be prefixed by their type
+   * - html-*.html
+   * - image-*.png, image-*.jpg and image-*.gif
+   * - javascript-*.txt and javascript-*.script
+   * - php-*.txt and php-*.php
+   * - sql-*.txt and sql-*.sql
+   *
+   * Subsequent calls will not generate new files or copy the files from
+   * core/modules/simpletest/files again. However, if a test class adds a new
+   * file to public:// that is prefixed with one of the above types,
+   * it will get returned as well, even on subsequent calls.
+   *
+   *
    * @param $type
    *   File type, possible values: 'binary', 'html', 'image', 'javascript',
    *   'php', 'sql', 'text'.
    * @param $size
-   *   File size in bytes to match. Please check the tests/files folder.
-   *
-   * @return
-   *   List of files that match filter.
+   *   (optional) File size in bytes to match. Defaults to NULL, which will not
+   *   filter the returned list by size. The files generated by this function
+   *   are of the following sizes (in bytes):
+   *   - binary: 16, 256, 1024, 2048, and 20480
+   *   - html: 24
+   *   - sql: 41
+   *   - php: 44, and 47
+   *   - javascript: 57, and 58
+   *   - text: 64, and 1024
+   *   - image: 125, 183, 964, 1831, 1901, and 39325
+   * @return array
+   *   List of files in public:// that match the filter(s).
    */
   protected function drupalGetTestFiles($type, $size = NULL) {
     if (empty($this->generatedTestFiles)) {