Add instructions for code coverage

.gitignore

@@ -86,3 +86,11 @@ Icon
 Network Trash Folder
 Temporary Items
 .apdisk
+
+# gcc coverage testing tool files
+*.gcno
+*.gcda
+*.gcov
+coverage.info
+/coverage
+

README.md

@@ -60,6 +60,21 @@ To run the tests with Clang sanitizers, run the following command from the root
 	./autogen.sh --enable-asan
 	make check
 
+### Code coverage
+
+Code coverage stats are generated with `lcov`. You can use [Homebrew](https://brew.sh/) on **OSX** to install the dependencies:
+
+	brew install lcov
+
+To run the tests with code coverage, run the following commands from the root of the repository:
+
+	./autogen.sh --enable-coverage
+	make check
+	lcov --capture --directory src --output-file coverage.info
+	genhtml coverage.info --output-directory coverage
+
+To view the coverage report, navigate to the `coverage` directory in the root of the repository and open `index.html`.
+
 ### Installing libgdiplus
 
 Run the following command from the root of the repository:

configure.ac

@@ -46,6 +46,13 @@ if test $asan = "yes"; then
   LDFLAGS="$LDFLAGS -fsanitize=address,signed-integer-overflow,undefined"
 fi
 
+AC_ARG_ENABLE(coverage, AS_HELP_STRING([--enable-coverage],[Enable code coverage.]),[coverage=yes],[coverage=no])
+
+if test $coverage = "yes"; then
+  GDIPLUS_CFLAGS="$GDIPLUS_CFLAGS --coverage -g"
+  LDFLAGS="$LDFLAGS --coverage"
+fi
+
 CAIRO_LIBS="`pkg-config --libs cairo `"
 CAIRO_CFLAGS="`pkg-config --cflags cairo `"
 cairo_info="`pkg-config --modversion cairo ` (system)"