Add tests for Series.format

Author: topper-123

pandas/core/strings.py

@@ -318,7 +318,7 @@ def str_format(
     3    Population: 21,477,737
     dtype: string
 
-    >>>  df.format("{state_name} ({state_abbreviation}): {population:,}")
+    >>> df.format("{state_name} ({state_abbreviation}): {population:,}")
     1    California (CA): 39,512,223
     2         Texas (TX): 28,995,881
     3       Florida (FL): 21,477,737

pandas/tests/series/methods/test_format.py

@@ -0,0 +1,64 @@
+import pytest
+
+import pandas as pd
+import pandas._testing as tm
+
+
+class TestFormat:
+    @pytest.mark.parametrize("format_str", ["Value: {}", "Value: {A}"])
+    @pytest.mark.parametrize("how_na", ["all", "any"])
+    def test_basic(self, format_str, how_na):
+        ser = pd.Series([1, 2, 3], name="A")
+        expected = pd.Series(
+            ["Value: 1", "Value: 2", "Value: 3"], dtype="string", name="X"
+        )
+
+        result = ser.format(format_str, how_na=how_na, name="X")
+        tm.assert_series_equal(result, expected)
+
+    @pytest.mark.parametrize("format_str", ["{Index}-{}", "{Index}-{A}"])
+    def test_with_index(self, format_str):
+        ser = pd.Series([1, 2, 3], name="A")
+        expected = pd.Series(["0-1", "1-2", "2-3"], dtype="string", name="X")
+
+        result = ser.format(format_str, name="X")
+        tm.assert_series_equal(result, expected)
+
+    @pytest.mark.parametrize("format_str", ["Value: {}"])
+    @pytest.mark.parametrize("positional_only", [True, False])
+    def test_positional_only(self, format_str, positional_only):
+        ser = pd.Series([1, 2, 3], name="A")
+        expected = pd.Series(["Value: 1", "Value: 2", "Value: 3"], dtype="string")
+
+        result = ser.format(format_str, positional_only=positional_only)
+        tm.assert_series_equal(result, expected)
+
+    @pytest.mark.parametrize("format_str", ["{A}-{}", "{Index}-{}"])
+    def test_positional_only_raises(self, format_str):
+        ser = pd.Series([1, 2, 3], name="A")
+        with pytest.raises(KeyError):
+            ser.format(format_str, positional_only=True)
+
+    @pytest.mark.parametrize(
+        "how_na, expected",
+        [("any", ["Value: 1", pd.NA, pd.NA]), ("all", ["Value: 1", pd.NA, pd.NA])],
+    )
+    @pytest.mark.parametrize("format_str", ["Value: {}", "Value: {A}"])
+    def test_na_how(self, how_na, expected, format_str):
+        ser = pd.Series([1, pd.NA, pd.NA], name="A")
+        expected = pd.Series(expected, dtype="string")
+
+        result = ser.format("Value: {}", how_na=how_na)
+        tm.assert_series_equal(result, expected)
+
+    @pytest.mark.parametrize("format_string", ["{}-{}", "{0}-{1}"])
+    def test_too_many_positional_args(self, format_string):
+        ser = pd.Series([1, 2, 3], name="A")
+        with pytest.raises(IndexError):
+            ser.format(format_string)
+
+    @pytest.mark.parametrize("format_string", ["{A}-{B}", "{B}"])
+    def test_unknown_named_args(self, format_string):
+        ser = pd.Series([1, 2, 3], name="A")
+        with pytest.raises(KeyError):
+            ser.format(format_string)