TST: add messages to bare pytest raises (#38414)

Author: Mark Graham

pandas/tests/generic/methods/test_pipe.py

@@ -31,5 +31,8 @@ def test_pipe_tuple_error(self, frame_or_series):
             obj = obj["A"]
 
         f = lambda x, y: y
-        with pytest.raises(ValueError):
+
+        msg = "y is both the pipe target and a keyword argument"
+
+        with pytest.raises(ValueError, match=msg):
             obj.pipe((f, "y"), x=1, y=0)

pandas/tests/reshape/merge/test_merge_asof.py

@@ -223,27 +223,29 @@ def test_multi_index(self):
         # MultiIndex is prohibited
         trades = self.trades.set_index(["time", "price"])
         quotes = self.quotes.set_index("time")
-        with pytest.raises(MergeError):
+        with pytest.raises(MergeError, match="left can only have one index"):
             merge_asof(trades, quotes, left_index=True, right_index=True)
 
         trades = self.trades.set_index("time")
         quotes = self.quotes.set_index(["time", "bid"])
-        with pytest.raises(MergeError):
+        with pytest.raises(MergeError, match="right can only have one index"):
             merge_asof(trades, quotes, left_index=True, right_index=True)
 
     def test_on_and_index(self):
 
         # "on" parameter and index together is prohibited
         trades = self.trades.set_index("time")
         quotes = self.quotes.set_index("time")
-        with pytest.raises(MergeError):
+        msg = 'Can only pass argument "left_on" OR "left_index" not both.'
+        with pytest.raises(MergeError, match=msg):
             merge_asof(
                 trades, quotes, left_on="price", left_index=True, right_index=True
             )
 
         trades = self.trades.set_index("time")
         quotes = self.quotes.set_index("time")
-        with pytest.raises(MergeError):
+        msg = 'Can only pass argument "right_on" OR "right_index" not both.'
+        with pytest.raises(MergeError, match=msg):
             merge_asof(
                 trades, quotes, right_on="bid", left_index=True, right_index=True
             )
@@ -439,7 +441,9 @@ def test_multiby_indexed(self):
 
         tm.assert_frame_equal(expected, result)
 
-        with pytest.raises(MergeError):
+        with pytest.raises(
+            MergeError, match="left_by and right_by must be same length"
+        ):
             pd.merge_asof(
                 left,
                 right,
@@ -478,13 +482,15 @@ def test_valid_join_keys(self):
         trades = self.trades
         quotes = self.quotes
 
-        with pytest.raises(MergeError):
+        msg = r"incompatible merge keys \[1\] .* must be the same type"
+
+        with pytest.raises(MergeError, match=msg):
             merge_asof(trades, quotes, left_on="time", right_on="bid", by="ticker")
 
-        with pytest.raises(MergeError):
+        with pytest.raises(MergeError, match="can only asof on a key for left"):
             merge_asof(trades, quotes, on=["time", "ticker"], by="ticker")
 
-        with pytest.raises(MergeError):
+        with pytest.raises(MergeError, match="can only asof on a key for left"):
             merge_asof(trades, quotes, by="ticker")
 
     def test_with_duplicates(self, datapath):
@@ -513,7 +519,9 @@ def test_valid_allow_exact_matches(self):
         trades = self.trades
         quotes = self.quotes
 
-        with pytest.raises(MergeError):
+        msg = "allow_exact_matches must be boolean, passed foo"
+
+        with pytest.raises(MergeError, match=msg):
             merge_asof(
                 trades, quotes, on="time", by="ticker", allow_exact_matches="foo"
             )
@@ -535,12 +543,14 @@ def test_valid_tolerance(self):
             tolerance=1,
         )
 
+        msg = r"incompatible tolerance .*, must be compat with type .*"
+
         # incompat
-        with pytest.raises(MergeError):
+        with pytest.raises(MergeError, match=msg):
             merge_asof(trades, quotes, on="time", by="ticker", tolerance=1)
 
         # invalid
-        with pytest.raises(MergeError):
+        with pytest.raises(MergeError, match=msg):
             merge_asof(
                 trades.reset_index(),
                 quotes.reset_index(),
@@ -549,13 +559,15 @@ def test_valid_tolerance(self):
                 tolerance=1.0,
             )
 
+        msg = "tolerance must be positive"
+
         # invalid negative
-        with pytest.raises(MergeError):
+        with pytest.raises(MergeError, match=msg):
             merge_asof(
                 trades, quotes, on="time", by="ticker", tolerance=-Timedelta("1s")
             )
 
-        with pytest.raises(MergeError):
+        with pytest.raises(MergeError, match=msg):
             merge_asof(
                 trades.reset_index(),
                 quotes.reset_index(),
@@ -572,13 +584,13 @@ def test_non_sorted(self):
         # we require that we are already sorted on time & quotes
         assert not trades.time.is_monotonic
         assert not quotes.time.is_monotonic
-        with pytest.raises(ValueError):
+        with pytest.raises(ValueError, match="left keys must be sorted"):
             merge_asof(trades, quotes, on="time", by="ticker")
 
         trades = self.trades.sort_values("time")
         assert trades.time.is_monotonic
         assert not quotes.time.is_monotonic
-        with pytest.raises(ValueError):
+        with pytest.raises(ValueError, match="right keys must be sorted"):
             merge_asof(trades, quotes, on="time", by="ticker")
 
         quotes = self.quotes.sort_values("time")