Refine message to `skip` in nested `assert`

- I think "Info" is used only to `skip`, so change to "Skip".
- Changed the default value of `assert` and specify the argument explicitly
  at the caller of `assert` because it is unnatural "Assertion failed" is
  output even though the assertion doesn't fail.

== Example:

  def assert_foo(exp, act)
    assert do
      assert_equal exp[0], act[0]
      assert_equal exp[1], act[1]
    end
  end

  def assert_bar(exp, act)
    assert do
      skip
    end
  end

  def assert_baz(exp, act)
    assert do
      assert_equal exp, act
      assert_bar exp, act
    end
  end

  assert 'test#skip_in_nested_assert' do
    assert_baz 1, 1
  end

  === Before this patch:

    ?..
    Info: test#skip_in_nested_assert (core)
     - Assertion[1]
        Info: Assertion failed (core)
         - Assertion[1-2]
            Skip: Assertion failed (core)
      Total: 3
         OK: 2
         KO: 0
      Crash: 0
    Warning: 0
       Skip: 1

  === After this patch:

    ???
    Skip: test#skip_in_nested_assert (core)
     - Assertion[1]
        Skip: assert (core)
         - Assertion[1-2]
            Skip: assert (core)
      Total: 3
         OK: 0
         KO: 0
      Crash: 0
    Warning: 0
       Skip: 3

5 files changed, 6 insertions, 6 deletions

diff --git a/mrbgems/mruby-bin-mruby/bintest/mruby.rb b/mrbgems/mruby-bin-mruby/bintest/mruby.rb
index 5dbbc5592..e032ff79a 100644
--- a/mrbgems/mruby-bin-mruby/bintest/mruby.rb
+++ b/mrbgems/mruby-bin-mruby/bintest/mruby.rb
@@ -3,7 +3,7 @@ require 'open3'
 
 def assert_mruby(exp_out, exp_err, exp_success, args)
   out, err, stat = Open3.capture3(cmd("mruby"), *args)
-  assert do
+  assert "assert_mruby" do
     assert_operator(exp_out, :===, out, "standard output")
     assert_operator(exp_err, :===, err, "standard error")
     assert_equal(exp_success, stat.success?, "exit success?")
diff --git a/mrbgems/mruby-complex/test/complex.rb b/mrbgems/mruby-complex/test/complex.rb
index 5b7c3bfa4..4ae80515b 100644
--- a/mrbgems/mruby-complex/test/complex.rb
+++ b/mrbgems/mruby-complex/test/complex.rb
@@ -1,5 +1,5 @@
 def assert_complex(real, exp)
-  assert do
+  assert "assert_complex" do
     assert_float real.real,      exp.real
     assert_float real.imaginary, exp.imaginary
   end
diff --git a/mrbgems/mruby-io/test/io.rb b/mrbgems/mruby-io/test/io.rb
index 1491a4cfe..3aaa109a8 100644
--- a/mrbgems/mruby-io/test/io.rb
+++ b/mrbgems/mruby-io/test/io.rb
@@ -5,7 +5,7 @@ MRubyIOTestUtil.io_test_setup
 $cr, $crlf, $cmd = MRubyIOTestUtil.win? ? [1, "\r\n", "cmd /c "] : [0, "\n", ""]
 
 def assert_io_open(meth)
-  assert do
+  assert "assert_io_open" do
     fd = IO.sysopen($mrbtest_io_rfname)
     assert_equal Fixnum, fd.class
     io1 = IO.__send__(meth, fd)
diff --git a/mrbgems/mruby-pack/test/pack.rb b/mrbgems/mruby-pack/test/pack.rb
index 68ef4165f..6832adcc7 100644
--- a/mrbgems/mruby-pack/test/pack.rb
+++ b/mrbgems/mruby-pack/test/pack.rb
@@ -2,7 +2,7 @@ PACK_IS_LITTLE_ENDIAN = "\x01\00".unpack('S')[0] == 0x01
 
 def assert_pack tmpl, packed, unpacked
   t = tmpl.inspect
-  assert do
+  assert "assert_pack" do
     assert_equal packed, unpacked.pack(tmpl), "#{unpacked.inspect}.pack(#{t})"
     assert_equal unpacked, packed.unpack(tmpl), "#{packed.inspect}.unpack(#{t})"
   end
diff --git a/mrbgems/mruby-rational/test/rational.rb b/mrbgems/mruby-rational/test/rational.rb
index 11737034b..a8ebb8ea2 100644
--- a/mrbgems/mruby-rational/test/rational.rb
+++ b/mrbgems/mruby-rational/test/rational.rb
@@ -23,14 +23,14 @@ class ComplexLikeNumeric < UserDefinedNumeric
 end
 
 def assert_rational(exp, real)
-  assert do
+  assert "assert_rational" do
     assert_float exp.numerator,   real.numerator
     assert_float exp.denominator, real.denominator
   end
 end
 
 def assert_equal_rational(exp, o1, o2)
-  assert do
+  assert "assert_equal_rational" do
     if exp
       assert_operator(o1, :==, o2)
       assert_not_operator(o1, :!=, o2)