diff --git a/tests/test_check.py b/tests/test_check.py
index 0ad968f..45b644b 100644
--- a/tests/test_check.py
+++ b/tests/test_check.py
@@ -4,20 +4,20 @@ import pandas as pd
 
 
 def test_check_invalid_issn(capsys):
-    '''Test checking invalid ISSN.'''
+    """Test checking invalid ISSN."""
 
-    value = '2321-2302'
+    value = "2321-2302"
 
     check.issn(value)
 
     captured = capsys.readouterr()
-    assert captured.out == f'Invalid ISSN: {value}\n'
+    assert captured.out == f"Invalid ISSN: {value}\n"
 
 
 def test_check_valid_issn():
-    '''Test checking valid ISSN.'''
+    """Test checking valid ISSN."""
 
-    value = '0024-9319'
+    value = "0024-9319"
 
     result = check.issn(value)
 
@@ -25,20 +25,20 @@ def test_check_valid_issn():
 
 
 def test_check_invalid_isbn(capsys):
-    '''Test checking invalid ISBN.'''
+    """Test checking invalid ISBN."""
 
-    value = '99921-58-10-6'
+    value = "99921-58-10-6"
 
     check.isbn(value)
 
     captured = capsys.readouterr()
-    assert captured.out == f'Invalid ISBN: {value}\n'
+    assert captured.out == f"Invalid ISBN: {value}\n"
 
 
 def test_check_valid_isbn():
-    '''Test checking valid ISBN.'''
+    """Test checking valid ISBN."""
 
-    value = '99921-58-10-7'
+    value = "99921-58-10-7"
 
     result = check.isbn(value)
 
@@ -46,20 +46,20 @@ def test_check_valid_isbn():
 
 
 def test_check_invalid_separators(capsys):
-    '''Test checking invalid multi-value separators.'''
+    """Test checking invalid multi-value separators."""
 
-    value = 'Alan|Orth'
+    value = "Alan|Orth"
 
     check.separators(value)
 
     captured = capsys.readouterr()
-    assert captured.out == f'Invalid multi-value separator: {value}\n'
+    assert captured.out == f"Invalid multi-value separator: {value}\n"
 
 
 def test_check_valid_separators():
-    '''Test checking valid multi-value separators.'''
+    """Test checking valid multi-value separators."""
 
-    value = 'Alan||Orth'
+    value = "Alan||Orth"
 
     result = check.separators(value)
 
@@ -67,50 +67,50 @@ def test_check_valid_separators():
 
 
 def test_check_missing_date(capsys):
-    '''Test checking missing date.'''
+    """Test checking missing date."""
 
     value = None
 
-    field_name = 'dc.date.issued'
+    field_name = "dc.date.issued"
 
     check.date(value, field_name)
 
     captured = capsys.readouterr()
-    assert captured.out == f'Missing date ({field_name}).\n'
+    assert captured.out == f"Missing date ({field_name}).\n"
 
 
 def test_check_multiple_dates(capsys):
-    '''Test checking multiple dates.'''
+    """Test checking multiple dates."""
 
-    value = '1990||1991'
+    value = "1990||1991"
 
-    field_name = 'dc.date.issued'
+    field_name = "dc.date.issued"
 
     check.date(value, field_name)
 
     captured = capsys.readouterr()
-    assert captured.out == f'Multiple dates not allowed ({field_name}): {value}\n'
+    assert captured.out == f"Multiple dates not allowed ({field_name}): {value}\n"
 
 
 def test_check_invalid_date(capsys):
-    '''Test checking invalid ISO8601 date.'''
+    """Test checking invalid ISO8601 date."""
 
-    value = '1990-0'
+    value = "1990-0"
 
-    field_name = 'dc.date.issued'
+    field_name = "dc.date.issued"
 
     check.date(value, field_name)
 
     captured = capsys.readouterr()
-    assert captured.out == f'Invalid date ({field_name}): {value}\n'
+    assert captured.out == f"Invalid date ({field_name}): {value}\n"
 
 
 def test_check_valid_date():
-    '''Test checking valid ISO8601 date.'''
+    """Test checking valid ISO8601 date."""
 
-    value = '1990'
+    value = "1990"
 
-    field_name = 'dc.date.issued'
+    field_name = "dc.date.issued"
 
     result = check.date(value, field_name)
 
@@ -118,22 +118,22 @@ def test_check_valid_date():
 
 
 def test_check_suspicious_characters(capsys):
-    '''Test checking for suspicious characters.'''
+    """Test checking for suspicious characters."""
 
-    value = 'foreˆt'
+    value = "foreˆt"
 
-    field_name = 'dc.contributor.author'
+    field_name = "dc.contributor.author"
 
     check.suspicious_characters(value, field_name)
 
     captured = capsys.readouterr()
-    assert captured.out == f'Suspicious character ({field_name}): ˆt\n'
+    assert captured.out == f"Suspicious character ({field_name}): ˆt\n"
 
 
 def test_check_valid_iso639_1_language():
-    '''Test valid ISO 639-1 (alpha 2) language.'''
+    """Test valid ISO 639-1 (alpha 2) language."""
 
-    value = 'ja'
+    value = "ja"
 
     result = check.language(value)
 
@@ -141,9 +141,9 @@ def test_check_valid_iso639_1_language():
 
 
 def test_check_valid_iso639_3_language():
-    '''Test valid ISO 639-3 (alpha 3) language.'''
+    """Test valid ISO 639-3 (alpha 3) language."""
 
-    value = 'eng'
+    value = "eng"
 
     result = check.language(value)
 
@@ -151,55 +151,55 @@ def test_check_valid_iso639_3_language():
 
 
 def test_check_invalid_iso639_1_language(capsys):
-    '''Test invalid ISO 639-1 (alpha 2) language.'''
+    """Test invalid ISO 639-1 (alpha 2) language."""
 
-    value = 'jp'
+    value = "jp"
 
     check.language(value)
 
     captured = capsys.readouterr()
-    assert captured.out == f'Invalid ISO 639-1 language: {value}\n'
+    assert captured.out == f"Invalid ISO 639-1 language: {value}\n"
 
 
 def test_check_invalid_iso639_3_language(capsys):
-    '''Test invalid ISO 639-3 (alpha 3) language.'''
+    """Test invalid ISO 639-3 (alpha 3) language."""
 
-    value = 'chi'
+    value = "chi"
 
     check.language(value)
 
     captured = capsys.readouterr()
-    assert captured.out == f'Invalid ISO 639-3 language: {value}\n'
+    assert captured.out == f"Invalid ISO 639-3 language: {value}\n"
 
 
 def test_check_invalid_language(capsys):
-    '''Test invalid language.'''
+    """Test invalid language."""
 
-    value = 'Span'
+    value = "Span"
 
     check.language(value)
 
     captured = capsys.readouterr()
-    assert captured.out == f'Invalid language: {value}\n'
+    assert captured.out == f"Invalid language: {value}\n"
 
 
 def test_check_invalid_agrovoc(capsys):
-    '''Test invalid AGROVOC subject.'''
+    """Test invalid AGROVOC subject."""
 
-    value = 'FOREST'
-    field_name = 'dc.subject'
+    value = "FOREST"
+    field_name = "dc.subject"
 
     check.agrovoc(value, field_name)
 
     captured = capsys.readouterr()
-    assert captured.out == f'Invalid AGROVOC ({field_name}): {value}\n'
+    assert captured.out == f"Invalid AGROVOC ({field_name}): {value}\n"
 
 
 def test_check_valid_agrovoc():
-    '''Test valid AGROVOC subject.'''
+    """Test valid AGROVOC subject."""
 
-    value = 'FORESTS'
-    field_name = 'dc.subject'
+    value = "FORESTS"
+    field_name = "dc.subject"
 
     result = check.agrovoc(value, field_name)
 
@@ -207,20 +207,20 @@ def test_check_valid_agrovoc():
 
 
 def test_check_uncommon_filename_extension(capsys):
-    '''Test uncommon filename extension.'''
+    """Test uncommon filename extension."""
 
-    value = 'file.pdf.lck'
+    value = "file.pdf.lck"
 
     check.filename_extension(value)
 
     captured = capsys.readouterr()
-    assert captured.out == f'Filename with uncommon extension: {value}\n'
+    assert captured.out == f"Filename with uncommon extension: {value}\n"
 
 
 def test_check_common_filename_extension():
-    '''Test common filename extension.'''
+    """Test common filename extension."""
 
-    value = 'file.pdf'
+    value = "file.pdf"
 
     result = check.filename_extension(value)
 
@@ -228,45 +228,51 @@ def test_check_common_filename_extension():
 
 
 def test_check_incorrect_iso_639_1_language(capsys):
-    '''Test incorrect ISO 639-1 language, as determined by comparing the item's language field with the actual language predicted in the item's title.'''
+    """Test incorrect ISO 639-1 language, as determined by comparing the item's language field with the actual language predicted in the item's title."""
 
-    title = 'A randomised vaccine field trial in Kenya demonstrates protection against wildebeest-associated malignant catarrhal fever in cattle'
-    language = 'es'
+    title = "A randomised vaccine field trial in Kenya demonstrates protection against wildebeest-associated malignant catarrhal fever in cattle"
+    language = "es"
 
     # Create a dictionary to mimic Pandas series
-    row = {'dc.title': title, 'dc.language.iso': language}
+    row = {"dc.title": title, "dc.language.iso": language}
     series = pd.Series(row)
 
     experimental.correct_language(series)
 
     captured = capsys.readouterr()
-    assert captured.out == f'Possibly incorrect language {language} (detected en): {title}\n'
+    assert (
+        captured.out
+        == f"Possibly incorrect language {language} (detected en): {title}\n"
+    )
 
 
 def test_check_incorrect_iso_639_3_language(capsys):
-    '''Test incorrect ISO 639-3 language, as determined by comparing the item's language field with the actual language predicted in the item's title.'''
+    """Test incorrect ISO 639-3 language, as determined by comparing the item's language field with the actual language predicted in the item's title."""
 
-    title = 'A randomised vaccine field trial in Kenya demonstrates protection against wildebeest-associated malignant catarrhal fever in cattle'
-    language = 'spa'
+    title = "A randomised vaccine field trial in Kenya demonstrates protection against wildebeest-associated malignant catarrhal fever in cattle"
+    language = "spa"
 
     # Create a dictionary to mimic Pandas series
-    row = {'dc.title': title, 'dc.language.iso': language}
+    row = {"dc.title": title, "dc.language.iso": language}
     series = pd.Series(row)
 
     experimental.correct_language(series)
 
     captured = capsys.readouterr()
-    assert captured.out == f'Possibly incorrect language {language} (detected eng): {title}\n'
+    assert (
+        captured.out
+        == f"Possibly incorrect language {language} (detected eng): {title}\n"
+    )
 
 
 def test_check_correct_iso_639_1_language():
-    '''Test correct ISO 639-1 language, as determined by comparing the item's language field with the actual language predicted in the item's title.'''
+    """Test correct ISO 639-1 language, as determined by comparing the item's language field with the actual language predicted in the item's title."""
 
-    title = 'A randomised vaccine field trial in Kenya demonstrates protection against wildebeest-associated malignant catarrhal fever in cattle'
-    language = 'en'
+    title = "A randomised vaccine field trial in Kenya demonstrates protection against wildebeest-associated malignant catarrhal fever in cattle"
+    language = "en"
 
     # Create a dictionary to mimic Pandas series
-    row = {'dc.title': title, 'dc.language.iso': language}
+    row = {"dc.title": title, "dc.language.iso": language}
     series = pd.Series(row)
 
     result = experimental.correct_language(series)
@@ -275,13 +281,13 @@ def test_check_correct_iso_639_1_language():
 
 
 def test_check_correct_iso_639_3_language():
-    '''Test correct ISO 639-3 language, as determined by comparing the item's language field with the actual language predicted in the item's title.'''
+    """Test correct ISO 639-3 language, as determined by comparing the item's language field with the actual language predicted in the item's title."""
 
-    title = 'A randomised vaccine field trial in Kenya demonstrates protection against wildebeest-associated malignant catarrhal fever in cattle'
-    language = 'eng'
+    title = "A randomised vaccine field trial in Kenya demonstrates protection against wildebeest-associated malignant catarrhal fever in cattle"
+    language = "eng"
 
     # Create a dictionary to mimic Pandas series
-    row = {'dc.title': title, 'dc.language.iso': language}
+    row = {"dc.title": title, "dc.language.iso": language}
     series = pd.Series(row)
 
     result = experimental.correct_language(series)
diff --git a/tests/test_fix.py b/tests/test_fix.py
index a589870..e6df205 100644
--- a/tests/test_fix.py
+++ b/tests/test_fix.py
@@ -2,67 +2,67 @@ import csv_metadata_quality.fix as fix
 
 
 def test_fix_leading_whitespace():
-    '''Test fixing leading whitespace.'''
+    """Test fixing leading whitespace."""
 
-    value = ' Alan'
+    value = " Alan"
 
-    assert fix.whitespace(value) == 'Alan'
+    assert fix.whitespace(value) == "Alan"
 
 
 def test_fix_trailing_whitespace():
-    '''Test fixing trailing whitespace.'''
+    """Test fixing trailing whitespace."""
 
-    value = 'Alan '
+    value = "Alan "
 
-    assert fix.whitespace(value) == 'Alan'
+    assert fix.whitespace(value) == "Alan"
 
 
 def test_fix_excessive_whitespace():
-    '''Test fixing excessive whitespace.'''
+    """Test fixing excessive whitespace."""
 
-    value = 'Alan  Orth'
+    value = "Alan  Orth"
 
-    assert fix.whitespace(value) == 'Alan Orth'
+    assert fix.whitespace(value) == "Alan Orth"
 
 
 def test_fix_invalid_separators():
-    '''Test fixing invalid multi-value separators.'''
+    """Test fixing invalid multi-value separators."""
 
-    value = 'Alan|Orth'
+    value = "Alan|Orth"
 
-    assert fix.separators(value) == 'Alan||Orth'
+    assert fix.separators(value) == "Alan||Orth"
 
 
 def test_fix_unnecessary_unicode():
-    '''Test fixing unnecessary Unicode.'''
+    """Test fixing unnecessary Unicode."""
 
-    value = 'Alan​ Orth'
+    value = "Alan​ Orth"
 
-    assert fix.unnecessary_unicode(value) == 'Alan Orth'
+    assert fix.unnecessary_unicode(value) == "Alan Orth"
 
 
 def test_fix_duplicates():
-    '''Test fixing duplicate metadata values.'''
+    """Test fixing duplicate metadata values."""
 
-    value = 'Kenya||Kenya'
+    value = "Kenya||Kenya"
 
-    assert fix.duplicates(value) == 'Kenya'
+    assert fix.duplicates(value) == "Kenya"
 
 
 def test_fix_newlines():
-    '''Test fixing newlines.'''
+    """Test fixing newlines."""
 
-    value = '''Ken
-ya'''
+    value = """Ken
+ya"""
 
-    assert fix.newlines(value) == 'Kenya'
+    assert fix.newlines(value) == "Kenya"
 
 
 def test_fix_comma_space():
-    '''Test adding space after comma.'''
+    """Test adding space after comma."""
 
-    value = 'Orth,Alan S.'
+    value = "Orth,Alan S."
 
-    field_name = 'dc.contributor.author'
+    field_name = "dc.contributor.author"
 
-    assert fix.comma_space(value, field_name) == 'Orth, Alan S.'
+    assert fix.comma_space(value, field_name) == "Orth, Alan S."