First test run executes less tests than subsequent runs

[jaeh]

This might be expected.

First run:

-------------------------------------------------------------------------------                                               
geometries visual tests
-------------------------------------------------------------------------------
../test/geometry_visual_test.cpp:250
...............................................................................                                               

../test/utils/geometry_equal.hpp:112: FAILED:
  REQUIRE( false )                                                                                                            
with messages:                                                                                                                
  mapnik::geometry::multi_polygon<double, std::vector>
  mapbox::geometry::polygon<double, std::vector>

===============================================================================
test cases:  202 |  201 passed | 1 failed
assertions: 1801 | 1800 passed | 1 failed

Subsequent runs:

-------------------------------------------------------------------------------                                               
geometries visual tests
-------------------------------------------------------------------------------
../test/geometry_visual_test.cpp:250
...............................................................................                                               

../test/utils/geometry_equal.hpp:112: FAILED:
  REQUIRE( false )                                                                                                            
with messages:                                                                                                                
  mapnik::geometry::multi_polygon<double, std::vector>
  mapbox::geometry::polygon<double, std::vector>

===============================================================================
test cases:  202 |  201 passed | 1 failed
assertions: 1903 | 1902 passed | 1 failed