diff -u b/core/modules/simpletest/simpletest.module b/core/modules/simpletest/simpletest.module
--- b/core/modules/simpletest/simpletest.module
+++ b/core/modules/simpletest/simpletest.module
@@ -490,17 +490,19 @@
  * Generates test file.
  *
  * @param string $filename
- *   The name of the file, including the path. The suffix ".txt" is appended
- *   to the supplied file name and the file is put into the public:// files directory.
+ *   The name of the file, including the path. The suffix ".txt" is appended to
+ *   the supplied file name and the file is put into the public:// files
+ *   directory.
  * @param int $width
  *   The number of characters on one line.
  * @param int $lines
  *   The number of lines in the file.
  * @param string $type
- *   (optional) The type, for example: "text", "binary", or "binary-text".
- *   If $type is "text", random ASCII characters are inserted into the file.
- *   If $type is "binary", random characters in the range of 0 to 31 are inserted into the file.
- *   The default value is "binary-text", and a random sequence of 0 and 1 values are inserted into the file.
+ *   (optional) The type, for example: "text", "binary", or "binary-text". If
+ *   $type is "text", random ASCII characters are inserted into the file. If
+ *   $type is "binary", random characters whose codes are in the range of 0 to
+ *   31 are inserted into the file. If $type is "binary-text" (default), a
+ *   random sequence of 0 and 1 values are inserted into the file.
  *
  * @return string
  *   The name of the file, including the path.
diff -u b/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
--- b/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -458,10 +458,11 @@
   /**
    * Gets a list of files that can be used in tests.
    *
-   * The first time this method is called, it will call simpletest_generate_file()
-   * to generate text and binary-text files in the public:// directory.
-   * It will also copy all files in core/modules/simpletest/files to public:// as well.
-   * These contain image, SQL, PHP, JavaScript and HTML files.
+   * The first time this method is called, it will call
+   * simpletest_generate_file() to generate text and binary-text files in the
+   * public:// directory. It will also copy all files in
+   * core/modules/simpletest/files to public://. These contain image, SQL, PHP,
+   * JavaScript and HTML files.
    *
    * All filenames are prefixed with their type and have appropriate extensions:
    * - text-*.txt