fizzbuzz/linked-list-and-binary-search-tree-c++/passoff/tut

Documentation TUT How-To minimum steps to make TUT work for you

What is TUT

TUT is a pure C++ unit test framework. Its name - TUT - stands for 
Template Unit Tests.

Features

TUT provides all features required for unit testing:

    * Similar tests can be grouped together into test groups. Each 
      test group has its unique name and is located in a separate 
      compilation unit. One group can contain almost unlimited number 
      of tests (actually, the limit is the compiler template 
      recursion depth).
    * User can run all the tests (regression), or just some selected 
      groups or even some tests in these groups.
    * TUT provides special template functions to check the condition 
      validity at run-time and to force test failure if required. 
      Since C++ doesn't provide a facility for obtaining stack trace 
      of the throwed exception and TUT avoids macros, those functions 
      accept string marker to allow users easely determine the source 
      of exception.
    * TUT contains callback that can be implemented by the calling code 
      to integrate with an IDE, for example. Callbacks tell listener 
      when a new test run started, when test runner switches to the 
      next tests group, when a test was completed (and what result it 
      has), and when test run was finished. The callbacks allow users 
      to produce their own visualization format for test process and results.
    * Being a template library, it doesn't need compilation; just 
      include the <tut.h> header into the test modules.

TUT tests organization

Test application

C++ produces executable code, so tests have to be compiled into a single 
binary called test application. The application can be built in automated 
mode to perform nightly tests. They also can be built manually when a 
developer hunts for bugs.

The test application contains tests, organized into test groups.

Test groups

The functionality of a tested application can be divided into a few separate 
function blocks (e.g. User Rights, Export, Processing, ...). It is natural 
to group together tests for each block. TUT invokes this test group. Each 
test group has a unique human-readable name and normally is located in a 
separate file.

Tests

Each single test usually checks only one specific element of functionality. 
For example, for a container a test could check whether size() call 
returns zero after the successful call to the clear() method.

Writing simple test

Preamble

You are going to create a new class for your application. You decided to 
write tests for the class to be sure it works while you are developing or, 
possibly, enhancing it. Let's consider your class is shared pointer: 
std::auto_ptr-alike type that shares the same object among instances.

Prior to test writing, you should decide what to test. Maximalist's 
approach requires to write so many tests that altering any single 
line of your production code will break at least one of them. 
Minimalist's approach allows one to write tests only for the most 
general or the most complex use cases. The truth lies somewhere in 
between, but only you, developer, know where. You should prepare 
common successful and unsuccessful scenarios, and the scenarios for 
testing any other functionality you believe might be broken in some way.

For our shared_ptr we obviosly should test constructors, assignment operators, referencing and passing ownership.

Skeleton

If you don't have any implemented class to test yet, it would be good to 
implement it as a set of stubs for a first time. Thus you'll get an 
interface, and be able to write your tests. Yes, that's correct: you 
should write your tests before writing code! First of all, writing tests 
often helps to understand oddities in the current interface, and fix it. 
Secondly, with the stubs all your tests will fail, so you'll be sure 
they do their job.

Creating Test Group

Since we're writing unit tests, it would be a good idea to group the 
tests for our class in one place to be able to run them separately. 
It's also natural in C++ to place all the grouped tests into one 
compilation unit (i.e. source file). So, to begin, we should create 
a new file. Let's call it test_shared_ptr.cpp. (Final variant of the 
test group can be found in examples/shared_ptr subdirectory of the 
distribution package)

// test_shared_ptr.cpp
#include <tut.h>

namespace tut
{
};
            

As you see, you need to include TUT header file (as expected) and 
use namespace tut for tests. You may also use anonymous namespace if 
your compiler allows it (you will need to instantiate methods from 
tut namespace and some compilers refuse to place such instantiations 
into the anonymous namespace).

A test group in TUT framework is described by the special template 
test_group<T>. The template parameter T is a type that will hold all 
test-specific data during the test execution. Actually, the data 
stored in T are member data of the test. Test object is inherited 
from T, so any test can refer to the data in T as its member data.

For simple test groups (where all data are stored in test local 
variables) type T is an empty struct.

#include <tut.h>

namespace tut
{
  struct shared_ptr_data
  { 
  };
}
            
But when tests have complex or repeating creation phase, you may put 
data members into the T and provide constructor (and, if required, 
destructor) for it. For each test, a new instance of T will be 
created. To prepare your test for execution TUT will use default 
constructor. Similarly, after the test has been finished, TUT 
calls the destructor to clean up T. I.e.:

#include <tut.h>

namespace tut
{
  struct complex_data
  {
    connection* con;
    complex_data(){ con = db_pool.get_connection(); }
    ~complex_data(){ db_pool.release_connection(con); }
  };

  // each test from now will have con data member initialized
  // by constructor:
  ...
  con->commit();
  ...
            

What will happen if the constructor throws an exception? TUT will treat 
it as if test itself failed with exception, so this test will 
not be executed. You'll see an exception mark near the test, and 
if the constructor throwed something printable, a certain message will appear.

Exception in destructor is threated a bit different. Reaching destruction 
phase means that the test is passed, so TUT marks test with warning 
status meaning that test itself was OK, but something bad has happend 
after the test.

Well, all we have written so far is just a type declaration. To work 
with a group we have to have an object, so we must create the test group 
object. Since we need only one test group object for each unit, we can 
(and should, actually) make this object static. To prevent name clash with 
other test group objects in the namespace tut, we should provide a 
descriptive name, or, alternatively, we may put it into the anonymous 
namespace. The former is more correct, but a descriptive name usually works 
well too, unless you're too terse in giving names to objects.

#include <tut.h>

namespace tut
{
    struct shared_ptr_data
    {

    };

    typedef test_group<shared_ptr_data> tg;
    tg shared_ptr_group("shared_ptr");
};
            
As you see, any test group accepts a single parameter - its human-readable 
name. This name is used to identify the group when a programmer wants to 
execute all tests or a single test within the group. So this name shall 
also be descriptive enough to avoid clashes. Since we're writing tests 
for a specific unit, it's enough to name it after the unit name.

Test group constructor will be called at unspecified moment at the test 
application startup. The constructor performs self-registration; it calls 
tut::runner and asks it to store the test group object name and location. 
Any other test group in the system undergoes the same processing, i.e. 
each test group object registers itself. Thus, test runner can iterate 
all test groups or execute any test group by its name.

Newly created group has no tests associated with it. To be more precise, 
it has predefined set of dummy tests. By default, there are 50 tests in a 
group, including dummy ones. To create a test group with higher volume 
(e.g. when tests are generated by a script and their number is higher) 
we must provide a higher border of test group size when it is instantiated:

#include <tut.h>

namespace tut
{
    struct huge_test_data
    {
    };

    // test group with maximum 500 tests
    typedef test_group<huge_test_data,500> testgroup;
    testgroup huge_test_testgroup("huge group");
};
            

Note also, that your compiler will possibly need a command-line switch 
or pragma to enlarge recursive instantiation depth. For g++, for 
example, you should specify at least --ftemplate-depth-501 to increase 
the depth. For more information see your compiler documentation.

Creating Tests

Now it's time to fill our test group with content.

In TUT, all tests have unique numbers inside the test group. Some 
people believe that textual names better describe failed tests in 
reports. I agree; but in reality C++ templates work good with numbers 
because they are compile-time constants and refuse to do the same 
with strings, since strings are in fact addresses of character 
buffers, i.e. run-time data.

As I mentioned above, our test group already has a few dummy tests; 
and we can replace any of them with something real just by writing 
our own version:

#include <tut.h>

namespace tut
{
    struct shared_ptr_data{};

    typedef test_group<shared_ptr_data> testgroup;
    typedef testgroup::object testobject;
    testgroup shared_ptr_testgroup("shared_ptr");

    template<>
    template<>
    void testobject::test<1>()
    {
        // do nothing test
    }
};
        

So far this test does nothing, but it's enough to illustrate the concept.

All tests in the group belong to the type test_group<T>::object. This 
class is directly inherited from our test data structure. In our case, it is

class object : public shared_ptr_data { ... }
        
This allows to access members of the data structure directly, since at 
the same time they are members of the object type. We also typedef the 
type with testobject for brevity.

We mark our test with number 1. Previously, test group had a dummy test 
with the same number, but now, since we've defined our own version, it 
replaces the dummy test as more specialized one. It's how C++ template 
ordering works.

The test we've written always succeeds. Successful test returns with no 
exceptions. Unsuccessful one either throws an exception, or fails at 
fail() or ensure() methods (which anyway just throw the exception when failed).

First real test

Well, now we know enough to write the first real working test. This test 
will create shared_ptr instances and check their state. We will define a 
small structure (keepee) to use it as shared_ptr stored object type.

#include <tut.h>
#include <shared_ptr.h>

namespace tut
{
    struct shared_ptr_data
    {
        struct keepee{ int data; };
    };

    typedef test_group<shared_ptr_data> testgroup;
    typedef testgroup::object testobject;
    testgroup shared_ptr_testgroup("shared_ptr");

    /**
     * Checks default constructor.
     */
    template<>
    template<>
    void testobject::test<1>()
    {
        shared_ptr<keepee> def;
        ensure("null",def.get() == 0);
    }
};
        

That's all! The first line creates shared_ptr. If constructor throws 
an exception, test will fail (exceptions, including '...', are catched 
by the TUT framework). If the first line succeeds, we must check 
whether the kept object is null one. To do this, we use test object 
member function ensure(), which throws std::logic_error with a given 
message if its second argument is not true. Finally, if destructor of 
shared_ptr fails with exception, TUT also will report this test as failed.

It's equally easy to write a test for the scenario where we expect to get 
an exception: let's consider our class should throw an exception if it 
has no stored object, and the operator -> is called.

/**
 * Checks operator -> throws instead of returning null.
 */
template<>
template<>
void testobject::test<2>()
{
    try
    {
        shared_ptr<keepee> sp;
        sp->data = 0;
        fail("exception expected");
    }
    catch( const std::runtime_error& ex )
    {
        // ok
    }
}
        

Here we expect the std::runtime_error. If operator doesn't throw it, 
we'll force the test to fail using another member function: fail(). It 
just throws std::logic_error with a given message. If operator throws 
anything else, our test will fail too, since we intercept only 
std::runtime_error, and any other exception means the test has failed.

NB: our second test has number 2 in its name; it can, actually, be any 
in range 1..Max; the only requirement is not to write tests with the 
same numbers. If you did, compiler will force you to fix them anyway.

And finally, one more test to demonstrate how to use the 
ensure_equals template member function:

/**
 * Checks keepee counting.
 */
template<>
template<>
void testobject::test<3>()
{
    shared_ptr<keepee> sp1(new keepee());
    shared_ptr<keepee> sp2(sp1);
    ensure_equals("second copy at sp1",sp1.count(),2);
    ensure_equals("second copy at sp2",sp2.count(),2);
}
        

The test checks if the shared_ptr correctly counts references during 
copy construction. What's interesting here is the template member 
ensure_equals. It has an additional functionality comparing with similar 
call ensure("second_copy",sp1.count()==2); it uses operator == to check 
the equality of the two passed parameters and, what's more important, it 
uses std::stream to format the passed parameters into a human-readable 
message (smth like: "second copy: expected 2, got 1"). It means that 
ensure_equals cannot be used with the types that don't have operator <<; 
but for those having the operator it provides much more informational message.

In contrast to JUnit assertEquals, where the expected value goes before 
the actual one, ensure_equals() accepts the expected after the actual 
value. I believe it's more natural to read ensure_equals("msg", count, 5) 
as "ensure that count equals to 5" rather than JUnit's 
"assert that 5 is the value of the count".

Running tests

Tests are already written, but an attempt to run them will be unsuccessful. 
We need a few other bits to complete the test application.

First of all, we need a main() method, simply because it must be in all 
applications. Secondly, we need a test runner singleton. Remember I said 
each test group should register itself in singleton? So, we need that 
singleton. And, finally, we need a kind of a callback handler to visualize 
our test results.

The design of TUT doesn't strictly set a way the tests are visualized; 
instead, it provides an opportunity to get the test results by means of 
callbacks. Moreover it allows user to output the results in any format he 
prefers. Of course, there is a "reference implementation" in the 
example/subdirectory of the project.

Test runner singleton is defined in tut.h, so all we need to activate it 
is to declare an object of the type tut::test_runner_singleton in the main 
module with a special name tut::runner.

Now, with the test_runner we can run tests. Singleton has method get() 
returning a reference to an instance of the test_runner class, which in 
turn has methods run_tests() to run all tests in all groups, 
run_tests(const std::string& groupname) to run all tests in a given group 
and run_test(const std::string& grp,int n) to run one test in the specified group.

// main.cpp
#include <tut.h>

namespace tut
{
    test_runner_singleton runner;
}

int main()
{
    // run all tests in all groups
    runner.get().run_tests();

    // run all tests in group "shared_ptr"
    runner.get().run_tests("shared_ptr");

    // run test number 5 in group "shared_ptr"
    runner.get().run_test("shared_ptr",5);

    return 0;
}
  
It's up to user to handle command-line arguments or GUI messages and map those 
arguments/messages to actual calls to test runner. Again, as you see, TUT 
doesn't restrict user here.

But, the last question is still unanswered: how do we get our test results? 
The answer lies inside tut::callback interface. User shall create its subclass, 
and write up to three simple methods. He also can omit any method since they 
have default no-op implementation. Each corresponding method is called in the 
following cases:

    * a new test run started;
    * test finished;
    * test run finished.

Here is a minimal implementation:

class visualizator : public tut::callback
{
public:
  void run_started(){ }

  void test_completed(const tut::test_result& tr)
  {
      // ... show test result here ...
  }

  void run_completed(){ }
};        

The most important is the test_completed() method; its parameter has type 
test_result, and contains everything about the finished test, from its group 
name and number to the exception message, if any. Member result is an enum 
that contains status of the test: ok, fail or ex. Take a look at the 
examples/basic/main.cpp for more complete visualizator.

Visualizator should be passed to the test_runner before run. Knowing that, 
we are ready to write the final version of our main module:

// main.cpp
#include <tut.h>

namespace tut
{
  test_runner_singleton runner;
}

class callback : public tut::callback
{
public:
  void run_started(){ std::cout << "\nbegin"; }

  void test_completed(const tut::test_result& tr)
  {
    std::cout << tr.test_pos << "=" << tr.result << std::flush;
  }

  void run_completed(){ std::cout << "\nend"; }
};

int main()
{
  callback clbk;
  runner.get().set_callback(&clbk);

  // run all tests in all groups
  runner.get().run_tests();
  return 0;
}
        
That's it. You are now ready to link and run our test application. Do it as often as possible; 
once a day is a definite must. I hope, TUT will help you to make your application more 
robust and relieve your testing pain. Feel free to send your questions, suggestions and 
critical opinions to me; I'll do my best to address them asap.