Fix dehumanize failing on singular time unit nouns

arrow/arrow.py

@@ -1412,6 +1412,10 @@ def dehumanize(self, input_string: str, locale: str = "en_us") -> "Arrow":
                 search_string = str(time_string)
                 search_string = search_string.format(r"\d+")
 
+                # Make trailing 's' optional so both "1 day" and "2 days" match
+                if search_string.endswith("s"):
+                    search_string = search_string[:-1] + "s?"
+
                 # Create search pattern and find within string
                 pattern = re.compile(rf"(^|\b|\d){search_string}")
                 match = pattern.search(input_string)

tests/test_arrow.py

@@ -2987,6 +2987,21 @@ def test_czech_slovak(self):
                 assert arw.dehumanize(past_string, locale=lang) == past
                 assert arw.dehumanize(future_string, locale=lang) == future
 
+    def test_singular_units(self):
+        arw = arrow.Arrow(2023, 1, 1)
+
+        assert arw.dehumanize("1 day ago") == arw.shift(days=-1)
+        assert arw.dehumanize("1 hour ago") == arw.shift(hours=-1)
+        assert arw.dehumanize("1 minute ago") == arw.shift(minutes=-1)
+        assert arw.dehumanize("1 second ago") == arw.shift(seconds=-1)
+        assert arw.dehumanize("1 week ago") == arw.shift(weeks=-1)
+        assert arw.dehumanize("1 month ago") == arw.shift(months=-1)
+        assert arw.dehumanize("1 year ago") == arw.shift(years=-1)
+
+        assert arw.dehumanize("in 1 day") == arw.shift(days=1)
+        assert arw.dehumanize("in 1 hour") == arw.shift(hours=1)
+        assert arw.dehumanize("in 1 minute") == arw.shift(minutes=1)
+
 
 class TestArrowIsBetween:
     def test_start_before_end(self):