diff --git a/R/file_mod.R b/R/file_mod.R
index 1b17af8..3f29018 100644
--- a/R/file_mod.R
+++ b/R/file_mod.R
@@ -8,6 +8,8 @@ parse_parameter_names <- function(filenames) {
 
   if(nrow(matches) == 0) {
     return(NULL)
+  } else if(length(filenames) == 1 && filenames[[1]] == "") { 
+    return(NULL)
   } else {
     return(unique(paste0(matches[,2], "_", matches[,3])))
   }
@@ -16,8 +18,10 @@ parse_parameter_names <- function(filenames) {
 #' Get publication IDs modified since a specified commit
 #'
 #' @param last_commit The commit ID to check to
-get_modified_files <- function(last_commit) {
-  sys_string <- paste0("git diff --name-only ", last_commit, " HEAD")
+get_modified_files <- function(last_commit, end_commit = "HEAD") {
+  end_commit <- paste0(" ", end_commit)
+
+  sys_string <- paste0("git diff --name-only ", last_commit, end_commit)
   files <- system(sys_string, intern = TRUE)
 
   modified_via_params <- files[startsWith(files, "parameters")] |>
diff --git a/tests/testthat/test-file-mod.R b/tests/testthat/test-file-mod.R
new file mode 100644
index 0000000..a97bebf
--- /dev/null
+++ b/tests/testthat/test-file-mod.R
@@ -0,0 +1,12 @@
+test_that("parse_parameter_names returns correct pub ID", {
+  expect_equal(parse_parameter_names("kozak_1988.csv"), "kozak_1988")
+
+  empty_parse <- parse_parameter_names("")
+  expect_true(is.null(empty_parse))
+})
+
+test_that("get_modified_files returns valid pub IDs", {
+  check <- get_modified_files("32006ca", "018e79d")
+
+  expect_equal(check, "sharma_2015")
+})
\ No newline at end of file
diff --git a/tests/testthat/test-publication-processing.R b/tests/testthat/test-publication-processing.R
index 7b831fe..82b274f 100644
--- a/tests/testthat/test-publication-processing.R
+++ b/tests/testthat/test-publication-processing.R
@@ -98,4 +98,4 @@ test_that("get_current_pub_ids_params returns valid publication ids", {
 
   # All pub_ids contain only characters before the year
   all(grepl("^[a-zA-Z]+_\\d{4}[a-zA-Z]?$", current_pub_ids))
-})
\ No newline at end of file
+})