test fixnum overflow for add, sub and mul

test/t/integer.rb

@@ -18,6 +18,14 @@ assert('Integer#+', '15.2.8.3.1') do
 
   assert_raise(TypeError){ 0+nil }
   assert_raise(TypeError){ 1+nil }
+
+  c = Mrbtest::FIXNUM_MAX + 1
+  d = Mrbtest::FIXNUM_MAX.__send__(:+, 1)
+  e = Mrbtest::FIXNUM_MAX + 1.0
+  assert_equal Float, c.class
+  assert_equal Float, d.class
+  assert_float e, c
+  assert_float e, d
 end
 
 assert('Integer#-', '15.2.8.3.2') do
@@ -26,6 +34,14 @@ assert('Integer#-', '15.2.8.3.2') do
 
   assert_equal 1, a
   assert_equal 1.0, b
+
+  c = Mrbtest::FIXNUM_MIN - 1
+  d = Mrbtest::FIXNUM_MIN.__send__(:-, 1)
+  e = Mrbtest::FIXNUM_MIN - 1.0
+  assert_equal Float, c.class
+  assert_equal Float, d.class
+  assert_float e, c
+  assert_float e, d
 end
 
 assert('Integer#*', '15.2.8.3.3') do
@@ -37,6 +53,14 @@ assert('Integer#*', '15.2.8.3.3') do
 
   assert_raise(TypeError){ 0*nil }
   assert_raise(TypeError){ 1*nil }
+
+  c = Mrbtest::FIXNUM_MAX * 2
+  d = Mrbtest::FIXNUM_MAX.__send__(:*, 2)
+  e = Mrbtest::FIXNUM_MAX * 2.0
+  assert_equal Float, c.class
+  assert_equal Float, d.class
+  assert_float e, c
+  assert_float e, d
 end
 
 assert('Integer#/', '15.2.8.3.4') do