diff --git a/tests/unit/maintainers_test.sh b/tests/unit/maintainers_test.sh
index 410719e8c..80a9bfc13 100755
--- a/tests/unit/maintainers_test.sh
+++ b/tests/unit/maintainers_test.sh
@@ -44,6 +44,9 @@ Maintainers already in 'To:' field of update_patch_test.patch"
 
 FAKE_KERNEL="tests/.tmp"
 
+# Original directory path to go back before each test function
+ORIGINAL_DIR="$PWD"
+
 function oneTimeSetUp()
 {
   # This creates tests/.tmp which should mock a kernel tree root. A .git
@@ -55,8 +58,9 @@ function oneTimeSetUp()
   cp -f tests/unit/samples/MAINTAINERS "$FAKE_KERNEL"/MAINTAINERS
   cp -f tests/unit/samples/external/get_maintainer.pl "$FAKE_KERNEL"/scripts/
   cp -f tests/unit/samples/update_patch_test{_model,}{,2}.patch "$FAKE_KERNEL"/
+  cp --force 'tests/unit/samples/cover_letter_test.patch' "$FAKE_KERNEL"
   cd "$FAKE_KERNEL" || {
-    fail "($LINENO) It was not possible to move to temporary directory"
+    fail "(${LINENO}) It was not possible to move to temporary directory"
     return
   }
   touch fs/some_file
@@ -66,7 +70,7 @@ function oneTimeSetUp()
   git config user.email kw@kw
   git commit --quiet -m "Test message"
   cd "$original_dir" || {
-    fail "($LINENO) It was not possible to move back from temp directory"
+    fail "(${LINENO}) It was not possible to move back from temp directory"
     return
   }
 
@@ -78,6 +82,27 @@ function oneTimeTearDown()
   rm -rf "$FAKE_KERNEL"
 }
 
+function setUp()
+{
+  # Ensure each test function starts running in ORIGINAL_DIR.
+  cd "$ORIGINAL_DIR" || {
+    fail "(${LINENO}) It was not possible to move to original dir"
+    return
+  }
+}
+
+function tearDown()
+{
+  # Check if SHUNIT_TMPDIR can be safely removed and then remove it and remake it.
+  is_safe_path_to_remove "$SHUNIT_TMPDIR"
+  if [[ "$?" == 0 ]]; then
+    rm --recursive --force "$SHUNIT_TMPDIR"
+    mkdir --parents "$SHUNIT_TMPDIR"
+  else
+    fail 'It was not possible to safely remove SHUNIT tmp directory.'
+  fi
+}
+
 function test_print_files_authors()
 {
   local -r ret=$(print_files_authors "tests/unit/samples/print_file_author_test_dir/code1.c")
@@ -93,13 +118,12 @@ function test_print_files_authors_from_dir()
 function test_maintainers_main()
 {
   local ret
-  local -r original_dir="$PWD"
 
   ret="$(maintainers_main tests/.tmp)"
   multilineAssertEquals "$ret" "$CORRECT_TMP_MSG"
 
   cd "$FAKE_KERNEL" || {
-    fail "($LINENO) It was not possible to move to temporary directory"
+    fail "(${LINENO}) It was not possible to move to temporary directory"
     return
   }
   ret="$(maintainers_main .)"
@@ -109,7 +133,7 @@ function test_maintainers_main()
   multilineAssertEquals "$CORRECT_TMP_FS_MSG" "$ret"
 
   cd fs || {
-    fail "($LINENO) It was not possible to move to fs directory"
+    fail "(${LINENO}) It was not possible to move to fs directory"
     return
   }
   ret="$(maintainers_main ..)"
@@ -117,49 +141,164 @@ function test_maintainers_main()
 
   ret="$(maintainers_main .)"
   multilineAssertEquals "$CORRECT_TMP_FS_MSG" "$ret"
-  cd "$original_dir" || {
-    fail "($LINENO) It was not possible to move back from temp directory"
+}
+
+# This function tests expected behaviors for failure in
+# parse_maintainers_options.
+function test_parse_maintainers_options()
+{
+  local return_status
+
+  cd "$FAKE_KERNEL" || {
+    fail "(${LINENO}) It was not possible to move to temporary directory"
     return
   }
+
+  # Invalid option (typo)
+  unset options_values
+  declare -gA options_values
+  parse_maintainers_options --update-pacth # Messy argument
+  return_status="$?"
+  assertEquals "(${LINENO})" 22 "$return_status"
+
+  # Invalid option (even with a correct one following it)
+  unset options_values
+  declare -gA options_values
+  parse_maintainers_options --update-patch --invalid-option
+  return_status="$?"
+  assertEquals "(${LINENO})" 22 "$return_status"
+
+  # Too many arguments
+  unset options_values
+  declare -gA options_values
+  parse_maintainers_options --update-patch '.' 'some_file'
+  return_status="$?"
+  assertEquals "(${LINENO})" 22 "$return_status"
+}
+
+function test_maintainers_main_update_patch_invalid_inputs()
+{
+  local return_status
+  local output_from_maintainers_main
+
+  cd "$FAKE_KERNEL" || {
+    fail "(${LINENO}) It was not possible to move to temporary directory"
+    return
+  }
+
+  output_from_maintainers_main="$(maintainers_main --update-patch 'fs/some_file')"
+  return_status="$?"
+  assertEquals "(${LINENO})" 'Option --update-patch was passed but given path is not a patch.' "$output_from_maintainers_main"
+  assertEquals "(${LINENO})" 1 "$return_status"
+
+  output_from_maintainers_main="$(maintainers_main --update-patch 'cover_letter_test.patch')"
+  return_status="$?"
+  assertEquals "(${LINENO})" 'Option --update-patch was passed but given path is not a patch.' "$output_from_maintainers_main"
+  assertEquals "(${LINENO})" 1 "$return_status"
+}
+
+# This function tests cases where the maintainers_main is called outside
+# of a kernel tree and the given path is not in a kernel tree either.
+function test_maintainers_main_no_kernel()
+{
+  local return_status
+  local output_from_maintainers_main
+
+  # Going outside of a kernel tree
+  cd "$SHUNIT_TMPDIR" || {
+    fail "(${LINENO}) It was not possible to move to temporary directory"
+    return
+  }
+  mkdir 'not-a-kernel'
+
+  # Testing with default value
+  output_from_maintainers_main="$(maintainers_main)"
+  return_status="$?"
+  assertEquals "(${LINENO})" 'Neither the given path nor the working path is in a kernel tree.' "$output_from_maintainers_main"
+  assertEquals "(${LINENO})" 1 "$return_status"
+
+  # Testing while giving a path
+  output_from_maintainers_main="$(maintainers_main ./not-a-kernel)"
+  return_status="$?"
+  assertEquals "(${LINENO})" 'Neither the given path nor the working path is in a kernel tree.' "$output_from_maintainers_main"
+  assertEquals "(${LINENO})" 1 "$return_status"
+}
+
+# This function tests cases where the maintainers_main is called inside
+# a kernel tree, but the given path is not a patch and is outside a kernel tree.
+function test_maintainers_main_path_out_of_tree()
+{
+  local return_status
+  local output_from_maintainers_main
+
+  cd "$FAKE_KERNEL" || {
+    fail "(${LINENO}) It was not possible to move to temporary directory"
+    return
+  }
+
+  output_from_maintainers_main="$(maintainers_main ..)"
+  return_status="$?"
+  assertEquals "(${LINENO})" 'The given file is not a patch and is outside a kernel tree.' "$output_from_maintainers_main"
+  assertEquals "(${LINENO})" 1 "$return_status"
+}
+
+# This function tests cases where the given paths to maintainers_main are invalid
+function test_maintainers_main_invalid_paths()
+{
+  local return_status
+  local output_from_maintainers_main
+
+  cd "$FAKE_KERNEL" || {
+    fail "(${LINENO}) It was not possible to move to temporary directory"
+    return
+  }
+
+  # Test for files that don't exist in current directory
+  output_from_maintainers_main="$(maintainers_main 'file-does-not-exist.c')"
+  return_status="$?"
+  assertEquals "(${LINENO})" 'Invalid path' "$output_from_maintainers_main"
+  assertEquals "(${LINENO})" 1 "$return_status"
+
+  # Test for files that don't exist in an other existing directory
+  output_from_maintainers_main="$(maintainers_main "$SHUNIT_TMPDIR/not-a-file.c")"
+  return_status="$?"
+  assertEquals "(${LINENO})" 'Invalid path' "$output_from_maintainers_main"
+  assertEquals "(${LINENO})" 1 "$return_status"
 }
 
 function test_maintainers_main_patch()
 {
-  local original_dir="$PWD"
+  local return_status
+
   cd "$FAKE_KERNEL" || {
-    fail "($LINENO) It was not possible to move to temporary directory"
+    fail "(${LINENO}) It was not possible to move to temporary directory"
     return
   }
 
-  ret="$(maintainers_main update_patch_test.patch)"
-  multilineAssertEquals "$CORRECT_TMP_MSG" "$ret"
+  return_status="$(maintainers_main update_patch_test.patch)"
+  multilineAssertEquals "$CORRECT_TMP_MSG" "$return_status"
 
   # test -u
   cp -f update_patch_test.patch{,.bak}
-  ret="$(maintainers_main -u update_patch_test.patch)"
-  multilineAssertEquals "$CORRECT_TMP_PATCH_MSG" "$ret"
+  return_status="$(maintainers_main -u update_patch_test.patch)"
+  multilineAssertEquals "$CORRECT_TMP_PATCH_MSG" "$return_status"
   assertFileEquals update_patch_test{,_model}.patch
   cp -f update_patch_test.patch{.bak,}
 
   # test --update-patch
-  ret="$(maintainers_main --update-patch update_patch_test.patch)"
-  multilineAssertEquals "$CORRECT_TMP_PATCH_MSG" "$ret"
+  return_status="$(maintainers_main --update-patch update_patch_test.patch)"
+  multilineAssertEquals "$CORRECT_TMP_PATCH_MSG" "$return_status"
   assertFileEquals update_patch_test{,_model}.patch
 
   # test for already existing maintainers
-  ret="$(maintainers_main -u update_patch_test.patch)"
-  multilineAssertEquals "$CORRECT_TMP_PATCH_ALREADY_IN_MSG" "$ret"
+  return_status="$(maintainers_main -u update_patch_test.patch)"
+  multilineAssertEquals "$CORRECT_TMP_PATCH_ALREADY_IN_MSG" "$return_status"
   assertFileEquals update_patch_test{,_model}.patch
 
   # test for already existing "To:" field without maintainers
-  ret="$(maintainers_main -u update_patch_test2.patch)"
-  multilineAssertEquals "$CORRECT_TMP_PATCH2_MSG" "$ret"
+  return_status="$(maintainers_main -u update_patch_test2.patch)"
+  multilineAssertEquals "$CORRECT_TMP_PATCH2_MSG" "$return_status"
   assertFileEquals update_patch_test{,_model}2.patch
-
-  cd "$original_dir" || {
-    fail "($LINENO) It was not possible to move back from temp directory"
-    return
-  }
 }
 
 invoke_shunit
diff --git a/tests/unit/samples/cover_letter_test.patch b/tests/unit/samples/cover_letter_test.patch
new file mode 100644
index 000000000..bc7398ff2
--- /dev/null
+++ b/tests/unit/samples/cover_letter_test.patch
@@ -0,0 +1,21 @@
+From 2741c6a546f4e0b148f7211def92a8843b9e0972 Mon Sep 17 00:00:00 2001
+From: kw <kw@example.net>
+Date: Fri, 23 May 2023 09:04:44 -0300
+Subject: [PATCH 0/2] Cover letter example
+
+This is an example of a cover letter for testing purposes.
+There are not actual pacthes related to this file and the
+following modified files do not exist.
+
+kw (2):
+  src: art3435: Add failure paths as corner cases
+  test: unit: art3435_test: Add failing tests
+  
+  src/art3435.c | 34 ++++++++++++++++++
+  test/unit/art3435.sh | 86 ++++++++++++++++++++++++++++++++++
+
+  2 files changed, 120 insertions(+)
+
+-- 
+2.34.1
+