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

2 files changed, 5 insertions, 5 deletions

diff --git a/test/assert.rb b/test/assert.rb
index 58ee4b913..5ae46ca70 100644
--- a/test/assert.rb
+++ b/test/assert.rb
@@ -76,7 +76,7 @@ end
 # iso : The ISO reference code of the feature
 #       which will be tested by this
 #       assertion
-def assert(str = 'Assertion failed', iso = '')
+def assert(str = 'assert', iso = '')
   t_print(str, (iso != '' ? " [#{iso}]" : ''), ' : ') if $mrbtest_verbose
   begin
     $mrbtest_child_noassert ||= [0]
@@ -99,10 +99,10 @@ def assert(str = 'Assertion failed', iso = '')
     yield
     if $mrbtest_assert.size > 0
       if $mrbtest_assert.size == $mrbtest_child_noassert[-1]
-        $asserts.push(assertion_string('Info: ', str, iso))
+        $asserts.push(assertion_string('Skip: ', str, iso))
         $mrbtest_child_noassert[-2] += 1
-        $ok_test += 1
-        t_print('.')
+        $skip_test += 1
+        t_print('?')
       else
         $asserts.push(assertion_string('Fail: ', str, iso))
         $ko_test += 1
diff --git a/test/t/numeric.rb b/test/t/numeric.rb
index bb95f8ef3..5b1e79153 100644
--- a/test/t/numeric.rb
+++ b/test/t/numeric.rb
@@ -8,7 +8,7 @@ def  assert_step(exp, receiver, args, inf: false)
     break if inf && exp.size == act.size
   end
   expr = "#{receiver.inspect}.step(#{args.map(&:inspect).join(', ')})"
-  assert do
+  assert "assert_step" do
     assert_true(exp.eql?(act), "#{expr}: counters", assertion_diff(exp, act))
     assert_same(receiver, ret, "#{expr}: return value") unless inf
   end