Revert "Remove tests that rely on MultiIndex merging."

This reverts commit 0ef8213.

python/cudf/cudf/tests/test_joining.py

@@ -1556,6 +1556,119 @@ def test_categorical_typecast_outer_one_cat(dtype):
     assert result["key"].dtype == left["key"].dtype.categories.dtype
 
 
+@pytest.mark.parametrize(
+    ("lhs", "rhs"),
+    [
+        (["a", "b"], ["a"]),
+        (["a"], ["a", "b"]),
+        (["a", "b"], ["b"]),
+        (["b"], ["a", "b"]),
+        (["a"], ["a"]),
+    ],
+)
+@pytest.mark.parametrize("how", ["left", "right", "outer", "inner"])
+@pytest.mark.parametrize("level", ["a", "b", 0, 1])
+def test_index_join(lhs, rhs, how, level):
+    l_pdf = pd.DataFrame({"a": [2, 3, 1, 4], "b": [3, 7, 8, 1]})
+    r_pdf = pd.DataFrame({"a": [1, 5, 4, 0], "b": [3, 9, 8, 4]})
+    l_df = cudf.from_pandas(l_pdf)
+    r_df = cudf.from_pandas(r_pdf)
+    p_lhs = l_pdf.set_index(lhs).index
+    p_rhs = r_pdf.set_index(rhs).index
+    g_lhs = l_df.set_index(lhs).index
+    g_rhs = r_df.set_index(rhs).index
+
+    expected = p_lhs.join(p_rhs, level=level, how=how).to_frame(index=False)
+    got = g_lhs.join(g_rhs, level=level, how=how).to_frame(index=False)
+
+    assert_join_results_equal(expected, got, how=how)
+
+
+def test_index_join_corner_cases():
+    l_pdf = pd.DataFrame({"a": [2, 3, 1, 4], "b": [3, 7, 8, 1]})
+    r_pdf = pd.DataFrame(
+        {"a": [1, 5, 4, 0], "b": [3, 9, 8, 4], "c": [2, 3, 6, 0]}
+    )
+    l_df = cudf.from_pandas(l_pdf)
+    r_df = cudf.from_pandas(r_pdf)
+
+    # Join when column name doesn't match with level
+    lhs = ["a", "b"]
+    # level and rhs don't match
+    rhs = ["c"]
+    level = "b"
+    how = "outer"
+    p_lhs = l_pdf.set_index(lhs).index
+    p_rhs = r_pdf.set_index(rhs).index
+    g_lhs = l_df.set_index(lhs).index
+    g_rhs = r_df.set_index(rhs).index
+    expected = p_lhs.join(p_rhs, level=level, how=how).to_frame(index=False)
+    got = g_lhs.join(g_rhs, level=level, how=how).to_frame(index=False)
+
+    assert_join_results_equal(expected, got, how=how)
+
+    # sort is supported only in case of two non-MultiIndex join
+    # Join when column name doesn't match with level
+    lhs = ["a"]
+    # level and rhs don't match
+    rhs = ["a"]
+    level = "b"
+    how = "left"
+    p_lhs = l_pdf.set_index(lhs).index
+    p_rhs = r_pdf.set_index(rhs).index
+    g_lhs = l_df.set_index(lhs).index
+    g_rhs = r_df.set_index(rhs).index
+    expected = p_lhs.join(p_rhs, how=how, sort=True)
+    got = g_lhs.join(g_rhs, how=how, sort=True)
+
+    assert_join_results_equal(expected, got, how=how)
+
+    # Pandas Index.join on categorical column returns generic column
+    # but cudf will be returning a categorical column itself.
+    lhs = ["a", "b"]
+    rhs = ["a"]
+    level = "a"
+    how = "inner"
+    l_df["a"] = l_df["a"].astype("category")
+    r_df["a"] = r_df["a"].astype("category")
+    p_lhs = l_pdf.set_index(lhs).index
+    p_rhs = r_pdf.set_index(rhs).index
+    g_lhs = l_df.set_index(lhs).index
+    g_rhs = r_df.set_index(rhs).index
+    expected = p_lhs.join(p_rhs, level=level, how=how).to_frame(index=False)
+    got = g_lhs.join(g_rhs, level=level, how=how).to_frame(index=False)
+
+    got["a"] = got["a"].astype(expected["a"].dtype)
+
+    assert_join_results_equal(expected, got, how=how)
+
+
+def test_index_join_exception_cases():
+    l_df = cudf.DataFrame({"a": [2, 3, 1, 4], "b": [3, 7, 8, 1]})
+    r_df = cudf.DataFrame(
+        {"a": [1, 5, 4, 0], "b": [3, 9, 8, 4], "c": [2, 3, 6, 0]}
+    )
+
+    # Join between two MultiIndex
+    lhs = ["a", "b"]
+    rhs = ["a", "c"]
+    level = "a"
+    how = "outer"
+    g_lhs = l_df.set_index(lhs).index
+    g_rhs = r_df.set_index(rhs).index
+
+    with pytest.raises(TypeError):
+        g_lhs.join(g_rhs, level=level, how=how)
+
+    # Improper level value, level should be an int or scalar value
+    level = ["a"]
+    rhs = ["a"]
+    g_lhs = l_df.set_index(lhs).index
+    g_rhs = r_df.set_index(rhs).index
+    with pytest.raises(ValueError):
+        g_lhs.join(g_rhs, level=level, how=how)
+
+
 def test_typecast_on_join_indexes():
     join_data_l = cudf.Series([1, 2, 3, 4, 5], dtype="int8")
     join_data_r = cudf.Series([1, 2, 3, 4, 6], dtype="int32")
@@ -2055,3 +2168,16 @@ def test_join_redundant_params():
         lhs.merge(rhs, right_on="a", left_index=True, right_index=True)
     with pytest.raises(ValueError):
         lhs.merge(rhs, left_on="c", right_on="b")
+
+
+def test_join_multiindex_index():
+    # test joining a MultiIndex with an Index with overlapping name
+    lhs = (
+        cudf.DataFrame({"a": [2, 3, 1], "b": [3, 4, 2]})
+        .set_index(["a", "b"])
+        .index
+    )
+    rhs = cudf.DataFrame({"a": [1, 4, 3]}).set_index("a").index
+    expect = lhs.to_pandas().join(rhs.to_pandas(), how="inner")
+    got = lhs.join(rhs, how="inner")
+    assert_join_results_equal(expect, got, how="inner")