Add test for parsing bump_multipler for normal map.

models/norm-texopt.mtl

@@ -0,0 +1,7 @@
+newmtl default
+Ka 0 0 0
+Kd 0 0 0
+Ks 0 0 0
+Kt 0.1 0.2 0.3
+norm -bm 3 normalmap.jpg
+

models/norm-texopt.obj

@@ -0,0 +1,7 @@
+mtllib norm-texopt.mtl
+o Test
+v 1.864151 -1.219172 -5.532511
+v 0.575869 -0.666304 5.896140
+v 0.940448 1.000000 -1.971128
+usemtl default
+f 1 2 3

tests/tester.cc

@@ -625,6 +625,24 @@ TEST_CASE("g_ignored", "[Issue138]") {
 
 }
 
+TEST_CASE("norm_texopts", "[norm]") {
+  tinyobj::attrib_t attrib;
+  std::vector<tinyobj::shape_t> shapes;
+  std::vector<tinyobj::material_t> materials;
+
+  std::string err;
+  bool ret = tinyobj::LoadObj(&attrib, &shapes, &materials, &err, "../models/norm-texopt.obj", gMtlBasePath);
+
+  if (!err.empty()) {
+    std::cerr << err << std::endl;
+  }
+  REQUIRE(true == ret);
+  REQUIRE(1 == shapes.size());
+  REQUIRE(1 == materials.size());
+  REQUIRE(3.0 == Approx(materials[0].normal_texopt.bump_multiplier));
+
+}
+
 #if 0
 int
 main(