Using Catch for Jeff Langr's TDD Book Chapter 2

As I'm a bit of a fan of Phil Nash's Catch test framework I decided to convert the code in Jeff Langr's book to use Catch. This post describes the changes that were required for the first tests, i.e. chapter 2.

Code for this project is here…

Basic changes

Catch is header only so is much simpler to incorporate than Google Mock/Test so the CMakeLists.txt can be much simpler. For the start of the chapter, this is sufficient:

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project(chapterFirstExample)
cmake_minimum_required(VERSION 2.6)

include_directories(../../Catch/include)
add_definitions(-std=c++0x)
set(CMAKE_CXX_FLAGS "${CMAXE_CXX_FLAGS} -Wall")

set(sources
   main.cpp
   SoundexTest.cpp)
add_executable(test ${sources})
target_link_libraries(test pthread)

All we need to do is change the path to the Catch include directory, remove the link path and remove the link libraries.

Similarly, main.cpp is also simpler:

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#define CATCH_CONFIG_MAIN
#include "catch.hpp"

Strictly speaking we don't need main.cpp at all, but it simplifies the test code to keep it.

First 4 examples

The first examples are not very challenging and all that needs to be changed is to #include "catch.hpp" and change the TEST macro for a TEST_CASE with quotes around the identifiers, e.g. example 4:

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#include <string>

class Soundex
{
public:
   std::string encode(const std::string& word) const {
      return "";
   }
};

#include "catch.hpp"

TEST_CASE("SoundexEncoding", "RetainsSoleLetterOfOneLetterWord") {
   Soundex soundex;

   auto encoded = soundex.encode("A");
}

Examples 5-7

Catch provides a much richer assertion mechanism so we can replace the ASSERT_THAT macro with a REQUIRE macro:

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//...
TEST_CASE("SoundexEncoding", "RetainsSoleLetterOfOneLetterWord") {
   Soundex soundex;

   auto encoded = soundex.encode("A");

   REQUIRE(encoded == "A");
}
Running this for example 5 gives the following output in Catch: 
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test.exe is a Catch v1.0 b23 host application.
Run with -? for options

-------------------------------------------------------------------------------
SoundexEncoding
-------------------------------------------------------------------------------
c:/Projects/git/jlangr/c2/SoundexTest.cpp:18
...............................................................................

c:/Projects/git/jlangr/c2/SoundexTest.cpp:24: FAILED:
  REQUIRE( encoded == "A" )
with expansion:
  "" == "A"

===============================================================================
1 test case - failed (1 assertion - failed)
As you can see, the output provides both the original expression and the reconstructed expression with the values the caused the assertion failure. Much better - Jeff’s explanation would have been much shorter with this! The fix in example 6 gives this output: 
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All tests passed (1 assertion in 1 test case)

In Catch, example 7 id identical to example 6 so has been removed.

Examples 9

This requires the same type of changes as above, except that the test case name needs to be unique…we'll fix that in example 10.

Example 10,11

We can use Catch SECTIONs to simplify this example…so we don't need the SoundexEncoding class at all, and the test looks like this:

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TEST_CASE("SoundexEncoding", "RetainsSoleLetterOfOneLetterWord") {
   Soundex soundex;

   SECTION("RetainsSoleLetterOfOneLetterWord") {
      auto encoded = soundex.encode("A");

      REQUIRE(encoded == "A000");
   }

   SECTION("PadsWithZerosToEnsureThreeDigits") {
      auto encoded = soundex.encode("I");

      REQUIRE(encoded == "I000");
   }
}

Catch will run the TEST_CASE for each SECTION, automatically initialising the soundex object on each run.

Example 11 is similar.

Examples 12-17

Example 12 requires similar changes, but fails (as expected):

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-------------------------------------------------------------------------------
SoundexEncoding
  ReplacesConsonantsWithAppropriateDigits
-------------------------------------------------------------------------------
c:/Projects/git/jlangr/c2/SoundexTest.cpp:7
...............................................................................

c:/Projects/git/jlangr/c2/SoundexTest.cpp:19: FAILED:
  REQUIRE( soundex.encode("Ab") == "A100" )
with expansion:
  "Ab000" == "A100"

Again, the output from Catch is much more helpful for diagnosing the error, providing the TEST_CASE name, the SECTION and the expansions.

Examples 13-17 follow the same pattern.

Examples 18-22

Examples 18-22 are similar but we can use the Catch CHECK() macro instead of EXPECT_THAT(), e.g.:

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   //...
   SECTION("ReplacesConsonantsWithAppropriateDigits") {
      CHECK(soundex.encode("Ab") == "A100");
      CHECK(soundex.encode("Ac") == "A200");
   }

Examples 23-25

In example 23, Jeff disables a test. We can't do the same thing with a Catch SECTION (yet…) but we can disable an entire test by using the '[hide]' tag, so we temporarily put the test in a TEST_CASE on its own:

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TEST_CASE("ReplacesMultipleConsonantsWithDigits", "[hide]") {
   Soundex soundex;
   REQUIRE(soundex.encode("Acdl") == "A234");
}

Example 26-31

In passing, note that Catch also detects the exception:

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SoundexEncoding
  LimitsLengthToFourCharacters
-------------------------------------------------------------------------------
c:/Projects/git/jlangr/c2/SoundexTest.cpp:5
...............................................................................

c:/Projects/git/jlangr/c2/SoundexTest.cpp:25: FAILED:
  REQUIRE( soundex.encode("Dcdlb").length() == 4u )
due to unexpected exception with message:
  basic_string::_S_create

Example 32

To use StartsWith in Catch, we must use the REQUIRE_THAT() macro, e.g.:

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   SECTION("UppercasesFirstLetter") {
      REQUIRE_THAT(soundex.encode("abcd"), StartsWith("A"));
   }

Examples 33-39

These all follow the same pattern as above.