Add more tests for the dataframe interchange protocol

protocol/tests/conftest.py

@@ -0,0 +1,11 @@
+import pytest
+import pandas as pd
+
+
+@pytest.fixture(scope="package")
+def df_from_dict():
+    def maker(dct, is_categorical=False):
+        df = pd.DataFrame(dct)
+        return df.astype("category") if is_categorical else df
+
+    return maker

protocol/tests/test_protocol.py

@@ -0,0 +1,147 @@
+import pytest
+import math
+import ctypes
+
+
+@pytest.mark.parametrize(
+    "test_data",
+    [
+        {"a": ["foo", "bar"], "b": ["baz", "qux"]},
+        {"a": [1.5, 2.5, 3.5], "b": [9.2, 10.5, 11.8]},
+        {"A": [1, 2, 3, 4], "B": [1, 2, 3, 4]},
+    ],
+    ids=["str_data", "float_data", "int_data"],
+)
+def test_only_one_dtype(test_data, df_from_dict):
+    columns = list(test_data.keys())
+    df = df_from_dict(test_data)
+    dfX = df.__dataframe__()
+
+    column_size = len(test_data[columns[0]])
+    for column in columns:
+        assert dfX.get_column_by_name(column).null_count == 0
+        assert dfX.get_column_by_name(column).size == column_size
+        assert dfX.get_column_by_name(column).offset == 0
+
+
+def test_float_int(df_from_dict):
+    df = df_from_dict(
+        {
+            "a": [1, 2, 3],
+            "b": [3, 4, 5],
+            "c": [1.5, 2.5, 3.5],
+            "d": [9, 10, 11],
+            "e": [True, False, True],
+            "f": ["a", "", "c"],
+        }
+    )
+    dfX = df.__dataframe__()
+    columns = {"a": 0, "b": 0, "c": 2, "d": 0, "e": 20, "f": 21}
+
+    for column, kind in columns.items():
+        colX = dfX.get_column_by_name(column)
+        assert colX.null_count == 0
+        assert colX.size == 3
+        assert colX.offset == 0
+
+        assert colX.dtype[0] == kind
+
+
+def test_na_float(df_from_dict):
+    df = df_from_dict({"a": [1.0, math.nan, 2.0]})
+    dfX = df.__dataframe__()
+    colX = dfX.get_column_by_name("a")
+    assert colX.null_count == 1
+
+
+def test_noncategorical(df_from_dict):
+    df = df_from_dict({"a": [1, 2, 3]})
+    dfX = df.__dataframe__()
+    colX = dfX.get_column_by_name("a")
+    with pytest.raises(TypeError):
+        colX.describe_categorical
+
+
+def test_categorical(df_from_dict):
+    df = df_from_dict(
+        {"weekday": ["Mon", "Tue", "Mon", "Wed", "Mon", "Thu", "Fri", "Sat", "Sun"]},
+        is_categorical=True,
+    )
+
+    colX = df.__dataframe__().get_column_by_name("weekday")
+    is_ordered, is_dictionary, _ = colX.describe_categorical
+    assert isinstance(is_ordered, bool)
+    assert isinstance(is_dictionary, bool)
+
+
+def test_dataframe(df_from_dict):
+    df = df_from_dict(
+        {"x": [True, True, False], "y": [1, 2, 0], "z": [9.2, 10.5, 11.8]}
+    )
+    dfX = df.__dataframe__()
+
+    assert dfX.num_columns() == 3
+    assert dfX.num_rows() == 3
+    assert dfX.num_chunks() == 1
+    assert list(dfX.column_names()) == ["x", "y", "z"]
+    assert (
+            list(dfX.select_columns((0, 2)).column_names())
+            == list(dfX.select_columns_by_name(("x", "z")).column_names())
+    )
+
+
+@pytest.mark.parametrize(["size", "n_chunks"], [(10, 3), (12, 3), (12, 5)])
+def test_df_get_chunks(size, n_chunks, df_from_dict):
+    df = df_from_dict({"x": list(range(size))})
+    dfX = df.__dataframe__()
+    chunks = list(dfX.get_chunks(n_chunks))
+    assert len(chunks) == n_chunks
+    assert sum(chunk.num_rows() for chunk in chunks) == size
+
+
+@pytest.mark.parametrize(["size", "n_chunks"], [(10, 3), (12, 3), (12, 5)])
+def test_column_get_chunks(size, n_chunks, df_from_dict):
+    df = df_from_dict({"x": list(range(size))})
+    dfX = df.__dataframe__()
+    chunks = list(dfX.get_column(0).get_chunks(n_chunks))
+    assert len(chunks) == n_chunks
+    assert sum(chunk.size for chunk in chunks) == size
+
+
+def test_get_columns(df_from_dict):
+    df = df_from_dict({"a": [0, 1], "b": [2.5, 3.5]})
+    dfX = df.__dataframe__()
+    for colX in dfX.get_columns():
+        assert colX.size == 2
+        assert colX.num_chunks() == 1
+    assert dfX.get_column(0).dtype[0] == 0
+    assert dfX.get_column(1).dtype[0] == 2
+
+
+def test_buffer(df_from_dict):
+    arr = [0, 1, -1]
+    df = df_from_dict({"a": arr})
+    dfX = df.__dataframe__()
+    colX = dfX.get_column(0)
+    bufX = colX.get_buffers()
+
+    dataBuf, dataDtype = bufX["data"]
+
+    assert dataBuf.bufsize > 0
+    assert dataBuf.ptr != 0
+    device, _ = dataBuf.__dlpack_device__
+
+    assert dataDtype[0] == 0
+
+    if device == 1:  # CPU-only as we're going to directly read memory here
+        bitwidth = dataDtype[1]
+        ctype = {
+            8: ctypes.c_int8,
+            16: ctypes.c_int16,
+            32: ctypes.c_int32,
+            64: ctypes.c_int64,
+        }[bitwidth]
+
+        for idx, truth in enumerate(arr):
+            val = ctype.from_address(dataBuf.ptr + idx * (bitwidth // 8)).value
+            assert val == truth, f"Buffer at index {idx} mismatch"