##

context("DFT calculations -- stats::fft [and fftw::FFT]")

library(stats)
has.fftw <- require(fftw)
if (!has.fftw) warning('fftw unavailable; please install to enable full testing capabilities.')

n. <- 10
x. <- seq_len(n.)
xn. <- 1.0*x.


test_that("stats::fft returns complex", {
  expect_is(fft(xn.), 'complex')
})

if (has.fftw){
  
  test_that("fftw::FFT returns complex", {
    expect_is(FFT(xn.), 'complex')
  })
  
  test_that("stats::fft and fftw::FFT return equivalent results", {
    
    # Forward transform
    expect_equal(fft(x.), FFT(xn.))
    expect_equal(fft(xn.), FFT(xn.))
    
    # Inverse transform
    # - by default FFTW scales the inverse transform so this is an error:
    expect_error(stopifnot(all.equal(fft(xn., inverse = TRUE), IFFT(xn.))))
    # but this is not:
    expect_equal(fft(xn., inverse = TRUE), IFFT(xn., scale=FALSE))
    
  })
}

##