title: When I run cxxtest I get an undefined reference error
body: <p>I'm not sure to understand the undefined reference I am getting.</p>
  
  <pre><code>./cxxtest/cxxtestgen.py -o tests.cpp --error-printer DrawTestSuite.h
  g++ -I./cxxtest/ -c tests.cpp
  g++ -o tests tests.o Color.o
  tests.o: In function `DrawTestSuite::testLinewidthOne()':
  tests.cpp:(.text._ZN13DrawTestSuite16t… undefined reference to `Linewidth::Linewidth(double)'
  tests.cpp:(.text._ZN13DrawTestSuite16t… undefined reference to `Linewidth::draw(std::basic_ostream&lt;char… std::char_traits&lt;char&gt; &gt;&amp;)'
  collect2: ld returned 1 exit status
  make: *** [tests] Error 1// DrawTestSuite.h
  </code></pre>
  
  <p>DrawTestSuite.h contains the unit-test and The test function calls on Linewidth.h to execute the constructer and member function draw.</p>
  
  <p>I have <code>#include "Linewidth.h"</code>in DrawTestSuite.h.</p>