expect_error(extract())
expect_error(extract(extract_vector = "derp"))
expect_error(extract(extract_matrix = "derp"))
expect_error(extract(extract_vector = "derp", extract_matrix = "derp"))
expect_error(extract(extract_vector = function() {}, extract_matrix = "derp"))
expect_error(extract(extract_vector = "derp", extract_matrix = function() {}))
expect_error(extract(extract_vector = function() {}, extract_matrix = function() {}))
expect_error(extract(extract_vector = function(x) {}, extract_matrix = function(x) {}))
expect_error(extract(extract_vector = function(x, i) {}, extract_matrix = function(x, i) {}))
expect_equal(typeof(extract(extract_vector = function(x, i) {}, extract_matrix = function(x, i, j) {})), "closure")
