+DocUnits are blocks of executable code placed in comments of modules, classes and properties.
+The execution can be verified using `assert`.
+
+Example with a class:
+
+ module foo
+ # var foo = new Foo
+ # assert foo.bar == 10
+ class Foo
+ var bar = 10
+ end
+
+Everything used in the test must be declared.
+To test a method you have to instantiate its class:
+
+ module foo
+ # var foo = new Foo
+ # assert foo.bar == 10
+ class Foo
+ # var foo = new Foo
+ # assert foo.baz(1, 2) == 3
+ fun baz(a, b: Int) do return a + b
+ end
+
+In a single piece of documentation, each docunit is considered a part of a single module, thus regrouped when
+tested.
+Therefore, it is possible (and recommended) to split docunits in small parts if it make the explanation easier.
+
+~~~~
+# Some example of grouped docunits
+#
+# Declare and initialize a variable `a`.
+#
+# var a = 1
+#
+# So the value of `a` can be used
+#
+# assert a == 1
+#
+# even in complex operations
+#
+# assert a + 1 == 2
+fun foo do end
+~~~~
+
+Sometime, some blocks of code has to be included in documentation but not considered by `nitunit`.
+Those blocks are distinguished by their tagged fences (untagged fences or fences tagged `nit` are considered to be docunits).
+
+~~~~
+# Some ASCII drawing
+#
+# ~~~~raw
+# @<
+# <__)
+# ~~~~
+fun foo do end
+~~~~
+
+The special fence-tag `nitish` could also be used to indicate pseudo-nit that will be ignored by nitunit but highlighted by nitdoc.
+Such `nitish` piece of code can be used to enclose examples that cannot compile or that one do not want to be automatically executed.
+
+~~~~
+# Some pseudo-nit
+#
+# ~~~~nitish
+# var a: Int = someting
+# # ...
+# if a == 1 then something else something-else
+# ~~~~
+#
+# Some code to not try to execute automatically
+#
+# ~~~~nitish
+# system("rm -rf /")
+# ~~~~
+~~~~
+
+The `nitunit` command is used to test Nit files:
+
+ $ nitunit foo.nit
+
+Groups (directories) can be given to test the documentation of the group and of all its Nit files:
+
+ $ nitunit lib/foo
+
+Finally, standard markdown documents can be checked with:
+
+ $ nitunit foo.md
+
+## Working with `TestSuites`
+
+TestSuites are Nit files that define a set of TestCases for a particular module.
+
+The test suite must be called `test_` followed by the name of the module to test.
+So for the module `foo.nit` the test suite will be called `test_foo.nit`.
+
+The structure of a test suite is the following:
+
+ # test suite for module `foo`
+ module test_foo
+ import foo # can be intrude to test private things
+ class TestFoo
+ # test case for `foo::Foo::baz`
+ fun test_baz do
+ var subject = new Foo
+ assert subject.baz(1, 2) == 3
+ end
+ end
+
+Test suite can be executed using the same `nitunit` command:
+
+ $ nitunit foo.nit
+
+`nitunit` will execute a test for each method named `test_*` in a class named `Test*`
+so multiple tests can be executed for a single method:
+
+ class TestFoo
+ fun test_baz_1 do
+ var subject = new Foo
+ assert subject.baz(1, 2) == 3
+ end
+ fun test_baz_2 do
+ var subject = new Foo
+ assert subject.baz(1, -2) == -1
+ end
+ end
+
+`TestSuites` also provide methods to configure the test run:
+
+`before_test` and `after_test`: methods called before/after each test case.
+They can be used to factorize repetitive tasks:
+
+ class TestFoo
+ var subject: Foo
+ # Mandatory empty init
+ init do end
+ # Method executed before each test
+ fun before_test do
+ subject = new Foo
+ end
+ fun test_baz_1 do
+ assert subject.baz(1, 2) == 3
+ end
+ fun test_baz_2 do
+ assert subject.baz(1, -2) == -1
+ end
+ end
+
+When using custom test attributes, an empty `init` must be declared to allow automatic test running.
+
+`before_module` and `after_module`: methods called before/after each test suite.
+They have to be declared at top level:
+
+ module test_bdd_connector
+ import bdd_connector
+ # Testing the bdd_connector
+ class TestConnector
+ # test cases using a server
+ end
+ # Method executed before testing the module
+ fun before_module do
+ # start server before all test cases
+ end
+ # Method executed after testing the module
+ fun after_module do
+ # stop server after all test cases
+ end
+
+## Generating test suites