Use nested `assert`

mrbgems/mruby-bin-mruby/bintest/mruby.rb

@@ -3,9 +3,11 @@ require 'open3'
 
 def assert_mruby(exp_out, exp_err, exp_success, args)
   out, err, stat = Open3.capture3(cmd("mruby"), *args)
+  assert do
     assert_operator(exp_out, :===, out, "standard output")
     assert_operator(exp_err, :===, err, "standard error")
     assert_equal(exp_success, stat.success?, "exit success?")
+  end
 end
 
 assert('regression for #1564') do

mrbgems/mruby-complex/test/complex.rb

 def assert_complex(real, exp)
+  assert do
     assert_float real.real,      exp.real
     assert_float real.imaginary, exp.imaginary
+  end
 end
 
 assert 'Complex' do

mrbgems/mruby-io/test/io.rb

@@ -5,6 +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
     fd = IO.sysopen($mrbtest_io_rfname)
     assert_equal Fixnum, fd.class
     io1 = IO.__send__(meth, fd)
@@ -23,6 +24,7 @@ def assert_io_open(meth)
       end
     end
     io2.close unless meth == :open
+  end
 end
 
 assert('IO.class', '15.2.20') do

mrbgems/mruby-pack/test/pack.rb

@@ -2,8 +2,10 @@ PACK_IS_LITTLE_ENDIAN = "\x01\00".unpack('S')[0] == 0x01
 
 def assert_pack tmpl, packed, unpacked
   t = tmpl.inspect
+  assert do
     assert_equal packed, unpacked.pack(tmpl), "#{unpacked.inspect}.pack(#{t})"
     assert_equal unpacked, packed.unpack(tmpl), "#{packed.inspect}.unpack(#{t})"
+  end
 end
 
 # pack & unpack 'm' (base64)

mrbgems/mruby-rational/test/rational.rb

@@ -23,11 +23,14 @@ class ComplexLikeNumeric < UserDefinedNumeric
 end
 
 def assert_rational(exp, real)
+  assert do
     assert_float exp.numerator,   real.numerator
     assert_float exp.denominator, real.denominator
+  end
 end
 
 def assert_equal_rational(exp, o1, o2)
+  assert do
     if exp
       assert_operator(o1, :==, o2)
       assert_not_operator(o1, :!=, o2)
@@ -35,6 +38,7 @@ def assert_equal_rational(exp, o1, o2)
       assert_not_operator(o1, :==, o2)
       assert_operator(o1, :!=, o2)
     end
+  end
 end
 
 def assert_cmp(exp, o1, o2)