add test cases of Thread class

execution of build/host/test/mrbtest makes segmentation fault on linux

test/thread.rb

@@ -4,3 +4,85 @@
 assert('Object.const_defined? :Thread') do
  Object.const_defined?(:Thread)
 end
+
+assert('Thread returns Fixnum') do
+  a = Thread.new{100}
+  a.join == 100
+end
+
+assert('Thread returns ture') do
+  a = Thread.new{true}
+  a.join == true
+end
+
+assert('Thread returns false') do
+  a = Thread.new{false}
+  a.join == false
+end
+
+assert('Thread returns Float') do
+  a = Thread.new{99.99}
+  a.join == 99.99
+end
+
+assert('Thread returns String') do
+  a = Thread.new{"hello"}
+  a.join == "hello"
+end
+
+assert('Thread returns Symbol') do
+  a = Thread.new{:hello}
+  a.join == :hello
+  true
+end
+
+assert('Thread returns Array') do
+  a = Thread.new{[1,2,3]}
+  a.join == [1,2,3]
+end
+
+assert('Thread returns Hash') do
+  a = Thread.new{{'abc_key' => 'abc_value', 'cba_key' => 'cba_value'}}
+  a.join == {'abc_key' => 'abc_value', 'cba_key' => 'cba_value'}
+end
+
+assert('Thread migrates Fixnum') do
+  a = Thread.new(100){|a| a}
+  a.join == 100
+end
+
+assert('Thread migrates ture') do
+  a = Thread.new(true){|a| a}
+  a.join == true
+end
+
+assert('Thread migrates false') do
+  a = Thread.new(false){|a| a}
+  a.join == false
+end
+
+assert('Thread migrates Float') do
+  a = Thread.new(99.99){|a| a}
+  a.join == 99.99
+end
+
+assert('Thread migrates String') do
+  a = Thread.new("hello"){|a| a}
+  a.join == "hello"
+end
+
+assert('Thread migrates Symbol') do
+  a = Thread.new(:hello){|a| a}
+  a.join == :hello
+  true
+end
+
+assert('Thread migrates Array') do
+  a = Thread.new([1,2,3]){|a| a}
+  a.join == [1,2,3]
+end
+
+assert('Thread migrates Hash') do
+  a = Thread.new({'abc_key' => 'abc_value', 'cba_key' => 'cba_value'}){|a| a}
+  a.join == {'abc_key' => 'abc_value', 'cba_key' => 'cba_value'}
+end