= Standard Sections

QED demos are light-weight specification documents, suitable
for Interface-driven Development. The documents are divided up into
clauses separated by blank lines. Clauses that are flush to the 
left margin are always explanation or comment clauses. Indented
clauses are always executable code.

Each code section is executed in order of appearance, within a
rescue wrapper that captures any failures or errors. If neither
a failure or error occur then the code gets a "pass".

For example, the following passes:

  (2 + 2).assert == 4

While the following would "fail", as indicated by the raising of 
an Assertion error:

  expect Assertion do
    (2 + 2).assert == 5
  end

And this would have raised a NameError:

  expect NameError do
    nobody_knows_method
  end


= Neutral Code

There is no means of specifying that a code clause is neutral code,
i.e. that it should be executed but not tested. Thus far, such a
feature has proven to be a YAGNI.


= Defining Custom Assertions

The context in which the QED code is run is a self-extended module, thus
reusable macros can be created simply by defining a method.

  def assert_integer(x)
    x.assert.is_a? Integer
  end

Now lets try out our new macro definition.

  assert_integer(4)

Let's prove that it can also fail:

  expect Assertion do
    assert_integer("IV")
  end


= Helper File

If you create a file called `qed_helper.rb` located in the directory with the
QED documents you are running via the `qed` command, it will be loaded first.
You can use that to load optional AE features, or define your own specialized
assertion methods.


= Before and After Clauses

QED supports *before* and *after* clauses in a specification
through the use of before and after code blocks. Before and after
clauses are executed at the beginning and at the end of each
subsequent step.

We use a *before* clause if we want to setup some code at the
start of each step.

  a, z = nil, nil

  before do
    a = "BEFORE"
  end

And an *after* clause to tear down objects after a step.

  after do
    z = "AFTER"
  end

Notice we assigned +a+ and +z+ before the block. This was to ensure
their visibility in the scope later. Now, lets verify this the *before*
and *after* clause work.

  a.assert == "BEFORE"

  a = "A"
  z = "Z"

And now.

  z.assert == "AFTER"

There can only be one before or after clause at a time. So if we
define a new *before* or *after* clause later in the document,
it will replace the current clause(s) in use.

As a demonstration of this:

  before do
    a = "BEFORE AGAIN"
  end

We will see it is the case.

  a.assert == "BEFORE AGAIN"

Only use *before* and *after* clauses when necessary --specifications
are generally more readable without them. Indeed, some developers
make a policy of avoiding them altogether. YMMV.


= Tabular Steps

Finally we will demonstrate a tabular step. +table+ method is used
for this. We supply a file name to the method telling QED where to
find the table data to be used in the test. All table files are looked
for relative to the location of the document. If no name is given the
'<doc-name>.yaml' is assumed.

The arity of the table block determines the number of columns each row
in the table should have. Each row is assigned in turn and run
through the coded step. Consider the following example:

Every row in 'table.yaml' will be assigned to the block parameters
and run through the following assertion.

  table do |x,y|
    x.upcase.assert == y
  end

This concludes the basic overview of QED's specification system, which
is itself a QED document. Yes, we eat our own dog food.

Q.E.D.

---
require 'qed_helper'