[ JDK VERSION : 1.6.* ]

Product Version: NetBeans IDE 6.8 Beta (Build 200910212001)
Java: 1.6.0_15; Java HotSpot(TM) 64-Bit Server VM 14.1-b02-92

It seems that "Rerun" performs all test methods but
remembers the number of test methods.

1. Create a Ruby project and create unit test like below.
   Just 1 test method.

class NewClassTest < Test::Unit::TestCase
  def test_myadd
    assert_equal(1,Sample.myadd(1,0))
  end
end

2. "Test File"

Result window shows "1 tests, 0 failures, 0 errors"

It's OK.

3. Add new method like

class NewClassTest < Test::Unit::TestCase
  def test_myadd
    assert_equal(1,Sample.myadd(1,0))
  end
  def test_myadd2
    assert_equal(2,Sample.myadd(1,1))
  end
end

4. Click "Rerun" icon

It will perform 2 methods but outputs is

"1 tests, 0 failures, 0 errors"

"2 tests" should be "1".

5. "Test File" again

"2 tests, 0 failures, 0 errors"

6. Rerun again

"2 tests, 0 failures, 0 errors"

So the number of tests will be reset when we perform "Test File". It's nice if it happens at "Rerun" action because
"Rerun" will perform all test methods.