Add tests section with enough docs to get started and some @todo for future possible sections

Author: SammyK

Book/index.rst

@@ -54,6 +54,20 @@ This part concerns only the PHP 7 branch. It is under development.
     php7/zend_engine.rst
     php7/final.rst
 
+Testing PHP Source
+------------------
+
+Writing tests applies to both PHP 5 & PHP 7.
+
+.. toctree::
+    :maxdepth: 3
+
+    tests/introduction.rst
+    tests/overview.rst
+    tests/running_the_test_suite.rst
+    tests/phpt_file_structure.rst
+    tests/examining_failed_test_output.rst
+
 Index and search
 ================
 

Book/tests/echo_basic.phpt

@@ -0,0 +1,8 @@
+--TEST--
+echo - basic test for echo language construct
+--FILE--
+<?php
+echo 'This works ', 'and takes args!';
+?>
+--EXPECT--
+This works and takes args!

Book/tests/examining_failed_test_output.rst

@@ -0,0 +1,12 @@
+.. _examining_failed_test_output:
+
+Examining failed test output
+============================
+
+We've learned how to create and run tests and have had great success with passing tests, but what happens when things go
+wrong? We'll examine how to help ourselves debug failed tests using the failed-test output files.
+
+Failed test output files
+------------------------
+
+@TODO Add all the rest here. :)

Book/tests/introduction.rst

@@ -0,0 +1,19 @@
+Testing with ``.phpt`` files
+============================
+
+Tests are a great way to get your foot in the door of PHP internals. You don't even need to know C in order to get
+started because all the tests are written in PHP.
+
+In this chapter we'll explore the test suite that covers the internal functionality of PHP. We'll cover everything from
+running the test suite with PHP's custom black-box testing tool called ``run-tests.php`` to creating new tests.
+
+@TODO
+-----
+
+The following sections still need to be written:
+
+* Examining failed test output (examining_failed_test_output)
+* Finding untested code (finding_untested_code)
+* Environment variables (advanced/environment_variables)
+* Redirect Tests (advanced/redirect_tests)
+* Step debugging with GDB (advanced/step_debugging_with_gdb)

Book/tests/overview.rst

@@ -0,0 +1,38 @@
+.. _overview:
+
+Testing overview
+================
+
+PHP has an extensive test suite with over 15,000 individual test files. The test files are run with PHP's black-box
+testing tool called `run-tests.php`_ which can be found in the root directory of the php source code.
+
+"But wait!" you say, "I heard that PHP source doesn't have any unit tests." You are correct. The PHP source code has
+zero unit tests. But it does have `functional tests`_ and lucky for us, these particular functional tests are written in
+PHP. The test files have a ``.phpt`` file extension and can be run just like any normal PHP file.
+
+The official documentation for writing phpt tests lives at `qa.php.net`_.
+
+.. _run-tests.php: https://github.com/php/php-src/blob/master/run-tests.php
+.. _`functional tests`: https://en.wikipedia.org/wiki/Functional_testing
+.. _`qa.php.net`: http://qa.php.net/write-test.php
+
+Black-box testing
+-----------------
+
+In a nutshell, `black-box testing`_ sends input to some function and examines the output after the function has finished
+execution. If the output matches what we were expecting, then the test has passed. Black-box testing doesn't care *how*
+something is done, it only cares about the end result. This is exactly how ``run-tests.php`` works; it takes a set of
+inputs, runs some PHP code and then examines the output. If the output matches what is expected, then the test passes.
+
+.. _black-box testing: https://en.wikipedia.org/wiki/Black-box_testing
+
+Where the test files live
+-------------------------
+
+The test files live in several different places throughout the codebase in folders named ``tests``. Each test folder
+contains ``.phpt`` files pertaining to its containing folder's code.
+
+* ``ext/{extension-name}/tests/`` Extension tests
+* ``sapi/{sapi-name}/tests/`` SAPI tests
+* ``Zend/tests/`` Zend engine tests
+* ``tests/`` More Zend engine tests