[CMake] Coverage -- What is happening when you run a binary more than once?

[Kent Williams]

For the NIfTI regression tests, we run a binary for each ADD_TEST -- 
i.e. we build, e.g. a program called nifti1_test.  Then each test is of 
the form

ADD_TEST(exampletest $(NIFTIUTILS_BINARY_DIR}/nifti1_test --testname 
exampletest)

There are about 10 different executions of nifti1_test every time you do 
a 'make test'.  When you have coverage turned on, doesn't each execution 
overwrite  the previous coverage data file?

If so, we're only getting coverage results for the last execution of 
nifti1_test, or am I missing something?