Add test for backward compatibility of double to string conversion

The testcase is ready to host more conversion tests but is currently
really only targetting the double-to-string.

refs mapnik#430, mapnik#1632

tests/cpp_tests/conversions_test.cpp

@@ -0,0 +1,76 @@
+#include <boost/version.hpp>
+#include <mapnik/util/conversions.hpp>
+#include <boost/detail/lightweight_test.hpp>
+#include <iostream>
+
+int main( int, char*[] )
+{
+    using mapnik::util::to_string;
+
+    std::string out;
+
+    // Test double
+
+    to_string(out, double(1));
+    BOOST_TEST_EQ( out,  "1" );
+    out.clear();
+
+    to_string(out, double(0.1));
+    BOOST_TEST_EQ( out,  "0.1" );
+    out.clear();
+
+    to_string(out, double(0.123));
+    BOOST_TEST_EQ( out,  "0.123" );
+    out.clear();
+
+    to_string(out, double(1e-06));
+    BOOST_TEST_EQ( out,  "1e-06" );
+    out.clear();
+
+    to_string(out, double(1e-05));
+    BOOST_TEST_EQ( out,  "0.00001" );
+    out.clear();
+
+    to_string(out, double(0.0001));
+    BOOST_TEST_EQ( out,  "0.0001" );
+    out.clear();
+
+    to_string(out, double(0.0001234567890123456));
+    BOOST_TEST_EQ( out,  "0.0001234567890123456" );
+    out.clear();
+
+    to_string(out, double(1000000000000000));
+    BOOST_TEST_EQ( out,  "1000000000000000" );
+    out.clear();
+
+    to_string(out, double(100000000000000.1));
+    BOOST_TEST_EQ( out,  "100000000000000.1" );
+    out.clear();
+
+    to_string(out, double(1.00001));
+    BOOST_TEST_EQ( out,  "1.00001" );
+    out.clear();
+
+    to_string(out, double(1234000000000000));
+    BOOST_TEST_EQ( out,  "1234000000000000" );
+    out.clear();
+
+    to_string(out, double(1.234e+16));
+    BOOST_TEST_EQ( out,  "1.234e+16" );
+    out.clear();
+
+    // Test int
+
+    to_string(out,   int(2));
+    BOOST_TEST_EQ( out, "2" );
+    out.clear();
+
+    if (!::boost::detail::test_errors()) {
+        std::clog << "C++ exceptions: \x1b[1;32m✓ \x1b[0m\n";
+#if BOOST_VERSION >= 104600
+        ::boost::detail::report_errors_remind().called_report_errors_function = true;
+#endif
+    } else {
+        return ::boost::report_errors();
+    }
+}