TraceSpy

def testing(a, b, c)
  raise 'heck' if a.is_a?(Numeric) && a > 20

  d = 5 if c.is_a?(Numeric) && c > 3

  a + b + c
end

testing_spy = TraceSpy::Method.new(:testing) do |spy|
  # On the arguments, given as keywords, will yield arguments to the block
  spy.on_arguments do |m|
    m.when(a: String, b: String, c: String) do |v|
      puts "Oh hey! You called me with strings: #{v}"
    end

    m.when(a: 1, b: 2, c: 3) do |v|
      puts "My args were 1, 2, 3: #{v}"
    end
  end

  # On an exception, will yield exception to the block
  spy.on_exception do |m|
    m.when(RuntimeError) do |e|
      puts "I encountered an error: #{e}"
    end
  end

  # On a return value, will yield the return to the block
  spy.on_return do |m|
    m.when(String) do |v|
      puts "Strings in, Strings out no?: #{v}. I got this in though: #{spy.current_arguments}"
    end

    m.when(:even?) do |v|
      puts "I got an even return: #{v}"
    end
  end

  # On a local variable being present:
  spy.on_locals do |m|
    m.when(d: 5) do |v|
      puts "I saw d was a local in here!: #{v}. I could also ask this: #{spy.current_local_variables}"
    end
  end
end

# If you want to manually enable/disable the trace, use:
#
#   testing_spy.enable
#   testing_spy.disable
#
# Otherwise, use:

# Outside of this block, the trace is inactive:
testing_spy.with_tracing do
  p testing(1, 2, 3)
  # My args were 1, 2, 3: {:a=>1, :b=>2, :c=>3}
  # I got an even return: 6
  # => 6

  p testing(21, 2, 3) rescue 'nope'
  # I encountered an error: heck
  # => 'nope'

  p testing(*%w(foo bar baz))
  # Oh hey! You called me with strings: {:a=>"foo", :b=>"bar", :c=>"baz"}
  # Strings in, Strings out no?: foobarbaz
  # => 'foobarbaz'

  p testing(1, 2, 4)
  # I saw d was a local in here!: {:a=>1, :b=>2, :c=>4, :d=>5}
  # => 7
end

# Back to normal
testing(1, 2, 3)
# => 6

gem 'trace_spy'