diff --git a/tests/testthat/test-substitute_letters.R b/tests/testthat/test-substitute_letters.R
index 2019e23..06cf3d7 100644
--- a/tests/testthat/test-substitute_letters.R
+++ b/tests/testthat/test-substitute_letters.R
@@ -1,99 +1,99 @@
-# SETUP ----
-sq_dna <- sq(c("ACTGTC", "CGCGTTA"), alphabet = "dna_bsc")
-sq_ami <- sq(c("APOPNIQEV", "CSVMIBF"), alphabet = "ami_ext")
-# sq_unt <- sq(c("GO%NC@E(123)RO", "NFI%(#)VT;"), alphabet = "unt")
-
-str_dna <- c("ACBGBC", "CGCGBBA")
-str_dna_num <- c("AC6G6C", "CGCG66A")
-str_ami <- c("AQWQXEQEV", "CSVZECF")
-str_ami_num <- c("A11O11NIQ3322", "CS22MI7F")
-
-# CORRECT PROTOTYPE OF RETURNED VALUE ----
-test_that("substitute_letters() returns an sq_atp object", {
-  expect_s3_class(substitute_letters(sq_dna, c(T = "B")),
-                  class = "sq_atp",
-                  exact = FALSE)
-  expect_s3_class(substitute_letters(sq_ami, c(P = "Q", O = "W", I = "E", U = "R", Y = "T", G = "V",
-                                               L = "A", K = "S", J = "D", H = "F", M = "Z", N = "X", B = "C")),
-                  class = "sq_atp",
-                  exact = FALSE)
-})
-
-test_that("substitute_letters() returns an object with trimmed alphabet attribute", {
-  expect_setequal(
-    alphabet(substitute_letters(sq_dna, c(T = "B"))),
-    c("A", "C", "G", "B", "-")
-  )
-  expect_setequal(
-    alphabet(substitute_letters(sq_ami, c(P = "Q", O = "W", I = "E", U = "R", Y = "T", G = "V",
-                                          L = "A", K = "S", J = "D", H = "F", M = "Z", N = "X", B = "C"))),
-    setdiff(alphabet(sq_ami), c("P", "O", "I", "U", "Y", "G", "L", "K", "J", "H", "M", "N", "B"))
-  )
-})
-
-test_that("substitute_letters() does not remove nor add sequences", {
-  expect_length(substitute_letters(sq_dna, c(T = "B")),
-                length(sq_dna))
-  expect_length(substitute_letters(sq_ami, c(P = "Q", O = "W", I = "E", U = "R", Y = "T", G = "V",
-                                             L = "A", K = "S", J = "D", H = "F", M = "Z", N = "X", B = "C")),
-                length(sq_ami))
-})
-
-test_that("substitute_letters() keep original_lengths unchanged", {
-  expect_equal(
-    get_sq_lengths(substitute_letters(sq_dna, c(T = "B"))),
-    get_sq_lengths(sq_dna)
-  )
-  expect_equal(
-    get_sq_lengths(substitute_letters(sq_ami, c(P = "Q", O = "W", I = "E", U = "R", Y = "T", G = "V",
-                                                L = "A", K = "S", J = "D", H = "F", M = "Z", N = "X", B = "C"))),
-    get_sq_lengths(sq_ami)
-  )
-})
-
-# ARGUMENT PREREQUISITES ----
-test_sq_only(substitute_letters, encoding = c(S = "H"))
-
-test_that("encoding must be either numeric or character", {
-  expect_error(substitute_letters(sq_dna, c(A = TRUE, T = FALSE)),
-               "encoding must be either numeric of character vector")
-  expect_error(substitute_letters(sq_dna, list(G = mean, C = sum)))
-})
-
-# CORRECT RETURN VALUE ----
-test_that("substitute_letters() correctly computes value", {
-  expect_equal(
-    as.character(substitute_letters(sq_dna, c(T = "B"))),
-    str_dna
-  )
-  expect_equal(
-    as.character(substitute_letters(sq_ami, c(P = "Q", O = "W", I = "E", U = "R", Y = "T", G = "V",
-                                              L = "A", K = "S", J = "D", H = "F", M = "Z", N = "X", B = "C"))),
-    str_ami
-  )
-})
-
-# COERCING NUMERIC VECTORS TO CHARACTERS ----
-test_that("substitute_letters() coerces numeric encodings to string vectors", {
-  expect_equal(
-    as.character(substitute_letters(sq_dna, c(T = 6))),
-    str_dna_num
-  )
-  expect_equal(
-    as.character(substitute_letters(sq_ami, c(P = 11, V = 22, E = 33, X = 6, B = 7))),
-    str_ami_num
-  )
-})
-
-# SURJECTIVITY OF SUBSTITUTION ----
-test_that("substitute_letters() is a surjection regarding the alphabets", {
-  expect_lte(
-    vec_size(alphabet(substitute_letters(sq_dna, c(T = "B")))),
-    vec_size(alphabet(sq_dna))
-  )
-  expect_lte(
-    vec_size(alphabet(substitute_letters(sq_ami, c(P = "Q", O = "W", I = "E", U = "R", Y = "T", G = "V",
-                                                   L = "A", K = "S", J = "D", H = "F", M = "Z", N = "X", B = "C")))),
-    vec_size(alphabet(sq_ami))
-  )
-})
+# SETUP ----
+sq_dna <- sq(c("ACTGTC", "CGCGTTA"), alphabet = "dna_bsc")
+sq_ami <- sq(c("APOPNIQEV", "CSVMIBF"), alphabet = "ami_ext")
+# sq_unt <- sq(c("GO%NC@E(123)RO", "NFI%(#)VT;"), alphabet = "unt")
+
+str_dna <- c("ACBGBC", "CGCGBBA")
+str_dna_num <- c("AC6G6C", "CGCG66A")
+str_ami <- c("AQWQXEQEV", "CSVZECF")
+str_ami_num <- c("A11O11NIQ3322", "CS22MI7F")
+
+# CORRECT PROTOTYPE OF RETURNED VALUE ----
+test_that("substitute_letters() returns an sq_atp object", {
+  expect_s3_class(substitute_letters(sq_dna, c(T = "B")),
+                  class = "sq_atp",
+                  exact = FALSE)
+  expect_s3_class(substitute_letters(sq_ami, c(P = "Q", O = "W", I = "E", U = "R", Y = "T", G = "V",
+                                               L = "A", K = "S", J = "D", H = "F", M = "Z", N = "X", B = "C")),
+                  class = "sq_atp",
+                  exact = FALSE)
+})
+
+test_that("substitute_letters() returns an object with trimmed alphabet attribute", {
+  expect_setequal(
+    alphabet(substitute_letters(sq_dna, c(T = "B"))),
+    c("A", "C", "G", "B", "-")
+  )
+  expect_setequal(
+    alphabet(substitute_letters(sq_ami, c(P = "Q", O = "W", I = "E", U = "R", Y = "T", G = "V",
+                                          L = "A", K = "S", J = "D", H = "F", M = "Z", N = "X", B = "C"))),
+    setdiff(as.character(alphabet(sq_ami)), c("P", "O", "I", "U", "Y", "G", "L", "K", "J", "H", "M", "N", "B"))
+  )
+})
+
+test_that("substitute_letters() does not remove nor add sequences", {
+  expect_length(substitute_letters(sq_dna, c(T = "B")),
+                length(sq_dna))
+  expect_length(substitute_letters(sq_ami, c(P = "Q", O = "W", I = "E", U = "R", Y = "T", G = "V",
+                                             L = "A", K = "S", J = "D", H = "F", M = "Z", N = "X", B = "C")),
+                length(sq_ami))
+})
+
+test_that("substitute_letters() keep original_lengths unchanged", {
+  expect_equal(
+    get_sq_lengths(substitute_letters(sq_dna, c(T = "B"))),
+    get_sq_lengths(sq_dna)
+  )
+  expect_equal(
+    get_sq_lengths(substitute_letters(sq_ami, c(P = "Q", O = "W", I = "E", U = "R", Y = "T", G = "V",
+                                                L = "A", K = "S", J = "D", H = "F", M = "Z", N = "X", B = "C"))),
+    get_sq_lengths(sq_ami)
+  )
+})
+
+# ARGUMENT PREREQUISITES ----
+test_sq_only(substitute_letters, encoding = c(S = "H"))
+
+test_that("encoding must be either numeric or character", {
+  expect_error(substitute_letters(sq_dna, c(A = TRUE, T = FALSE)),
+               "encoding must be either numeric of character vector")
+  expect_error(substitute_letters(sq_dna, list(G = mean, C = sum)))
+})
+
+# CORRECT RETURN VALUE ----
+test_that("substitute_letters() correctly computes value", {
+  expect_equal(
+    as.character(substitute_letters(sq_dna, c(T = "B"))),
+    str_dna
+  )
+  expect_equal(
+    as.character(substitute_letters(sq_ami, c(P = "Q", O = "W", I = "E", U = "R", Y = "T", G = "V",
+                                              L = "A", K = "S", J = "D", H = "F", M = "Z", N = "X", B = "C"))),
+    str_ami
+  )
+})
+
+# COERCING NUMERIC VECTORS TO CHARACTERS ----
+test_that("substitute_letters() coerces numeric encodings to string vectors", {
+  expect_equal(
+    as.character(substitute_letters(sq_dna, c(T = 6))),
+    str_dna_num
+  )
+  expect_equal(
+    as.character(substitute_letters(sq_ami, c(P = 11, V = 22, E = 33, X = 6, B = 7))),
+    str_ami_num
+  )
+})
+
+# SURJECTIVITY OF SUBSTITUTION ----
+test_that("substitute_letters() is a surjection regarding the alphabets", {
+  expect_lte(
+    vec_size(alphabet(substitute_letters(sq_dna, c(T = "B")))),
+    vec_size(alphabet(sq_dna))
+  )
+  expect_lte(
+    vec_size(alphabet(substitute_letters(sq_ami, c(P = "Q", O = "W", I = "E", U = "R", Y = "T", G = "V",
+                                                   L = "A", K = "S", J = "D", H = "F", M = "Z", N = "X", B = "C")))),
+    vec_size(alphabet(sq_ami))
+  )
+})