[newbie] assert_writes implementation

[Alexey Verkhovsky]

Context: I needed to teach a subclass of Test::Unit::TestCase to assert
that a particular block writes something to an output stream.

In Java, an easy way to do something like this is with a pair of
PipedOutputStream/PipedInputStream pair. So I tried the same thing in
Ruby, and the result looks bit hairy to me. Having to use multi-process
semantics to write top a buffer and then read from it is a bit over the
top. There must be some better way.

Here is my code:

def assert_writes(expectedOutput)
reader, writer = IO.pipe

if fork
begin
writer.close
output = reader.read
ensure
reader.close if (reader && !reader.closed?)
end
Process.wait
assert_equal(expectedOutput, output)
else
begin
reader.close
yield(writer)
ensure
writer.close if (writer && !writer.closed?)
end
end
end

# usage example
def test_display
assert_writes("aaa") {|outputStream| "aaa".display(outputStream)}
end

Please be so kind to tell me:

1. Is it normal to do it this way?

2. Is it the right way to do it? I am not sure this code handles all
exception paths correctly.

3. Rdoc says that "IO#pipe" is not supported on all platforms. So, is
there a portable way to do it?

Brgds,
Alexey Verkhovsky

 

[Nathaniel Talbott]

Context: I needed to teach a subclass of Test::Unit::TestCase to
assert that a particular block writes something to an output stream.

In Java, an easy way to do something like this is with a pair of
PipedOutputStream/PipedInputStream pair. So I tried the same thing in
Ruby, and the result looks bit hairy to me. Having to use
multi-process semantics to write top a buffer and then read from it is
a bit over the top. There must be some better way.

Would StringIO help?
(http://www.ruby-doc.org/stdlib/libdoc/stringio/rdoc/index.html)

require 'test/unit'

require 'stringio'

class TestAssertWrite < Test::Unit::TestCase
def assert_write(expected)
io = StringIO.new
yield(io)
assert_equal(expected, io.string)
end

def test_assert_write
assert_raise(Test::Unit::AssertionFailedError) do
assert_write("expected") do |output|
output.write("bogus")
end
end
assert_nothing_raised do
assert_write("expected") do |output|
output.write("expected")
end
end
end
end


Nathaniel
Terralien, Inc.

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[Alexey Verkhovsky]

Would StringIO help?

Yup, that's the thing I was looking for! Thanks for enlightening me.

Alex