Move arrow-pyarrow tests that require pyarrow to be installed into arrow-pyarrow-testing crate (#7742)

# Which issue does this PR close?

- Related to #7394
- Closes #7736

# Rationale for this change

At its core, if someone isn't using / modifying the pyarrow integration
for arrow-rs they shouldn't have to install / configure python to get
the tests working in `arrow-rs`

- after the change in #7694

Running `cargo test --workspace` now also runs tests that require python
to be setup and the `pyarrow` module to be installed. This is
problematic because:
1. Some people may not have that environment setup
2. Apparently you can not use virtualenvs with py03 in Mac due to
PyO3/pyo3#1741

The second item was very confusing for me while I tried to debug what
going on as I ket getting an error about pyarrow not being installed,
even though it was installed in my `venv`:

```
thread 'test_to_pyarrow' panicked at arrow-pyarrow/tests/pyarrow.rs:43:6:
called `Result::unwrap()` on an `Err` value: PyErr { type: <class 'ModuleNotFoundError'>, value: ModuleNotFoundError("No module named 'pyarrow'"), traceback: None }
```

# What changes are included in this PR?

1. Move the tests that require pyarrow to be installed into
`arrow-pyarrow-testing`, which is not part of the workspace and thus not
run with `cargo test --all`
2. Remove `cargo test --exclude arrow-pyarrow`
3. Add documentation on rationale and hints about running the test

# Frequently Asked Questions

## Why not add ` --exclude arrow-pyarrow` to
`verify_release_candidate.sh`?

While the minimal fix would be to add ` --exclude arrow-pyarrow` to
verify_release_candidate.sh this requires all users of arrow to remember
to add `--exclude arrow-pyarrow` to their tests even if they don't care
about python

## Why not in `pyarrow-arrow-integration-testing` ?
I did not put this test in `pyarrow-arrow-integration-testing` because
that module doesn't compile for me with the stock python install

Somehow python needs to be installed with the ability to make dynamic
libraries that I haven't figured out and don't really want to. It seems
maybe related to https://pyo3.rs/v0.18.1/getting_started#python (thanks
to @Xuanwo for the pointer in PyO3/pyo3#2136 /
apache/opendal#1675)


```
(venv) root@5e8d0406fabe:/arrow-rs/arrow-pyarrow-integration-testing# cargo test --test pyarrow
warning: `/arrow-rs/arrow-pyarrow-integration-testing/.cargo/config` is deprecated in favor of `config.toml`
note: if you need to support cargo 1.38 or earlier, you can symlink `config` to `config.toml`
   Compiling target-lexicon v0.13.2
   Compiling flatbuffers v25.2.10
   Compiling pyo3-build-config v0.24.2
   Compiling arrow-ipc v55.2.0 (/arrow-rs/arrow-ipc)
   Compiling pyo3-macros-backend v0.24.2
   Compiling pyo3-ffi v0.24.2
   Compiling pyo3 v0.24.2
   Compiling pyo3-macros v0.24.2
   Compiling arrow-pyarrow v55.2.0 (/arrow-rs/arrow-pyarrow)
   Compiling arrow v55.2.0 (/arrow-rs/arrow)
   Compiling arrow-pyarrow-integration-testing v0.1.0 (/arrow-rs/arrow-pyarrow-integration-testing)
error: linking with `cc` failed: exit status: 1
  |
  = note:  "cc" "/tmp/rustc0jx15I/symbols.o" "<43 object files omitted>" "-Wl,--as-needed" "-Wl,-Bstatic" "<sysroot>/lib/rustlib/aarch64-unknown-linux-gnu/lib/{libtest-*,libgetopts-*,libunicode_width-*,librustc_std_workspace_std-*}.rlib" "/arrow-rs/arrow-pyarrow-integration-testing/target/debug/deps/{libarrow-7996898a6777f964.rlib,libarrow_row-63508de6e52f4d4d.rlib,libarrow_pyarrow-8b510eeadc952ad2.rlib,libpyo3-c463c3a2243eeab9.rlib,libmemoffset-836dc1ddd866c614.rlib,libpyo3_ffi-fbf18d9f712874be.rlib,libunindent-2b8a456e13fa9700.rlib,libarrow_json-a7b4960a4b4d1cb5.rlib,libsimdutf8-7e080cbee40e41cd.rlib,libserde_json-0288fe0f1ec1bcde.rlib,libindexmap-ebb707a4eec26692.rlib,libequivalent-4762261bc2781d11.rlib,libarrow_ipc-085ebaaded386ff8.rlib,libflatbuffers-1f88fdf138129305.rlib,libarrow_csv-e5d679eef2b85a1b.rlib,libcsv-2288f6dec5308d9c.rlib,libitoa-fa5c9b2503c605f5.rlib,libserde-33ccdec93d601cce.rlib,libcsv_core-122def45831e6a2c.rlib,libarrow_string-17ebd7a5409511da.rlib,libregex-97f4021e65bafbca.rlib,libregex_automata-b62a0db5ace54d45.rlib,libaho_corasick-547ec01718db652c.rlib,libregex_syntax-f3065c7bb7c4592a.rlib,libmemchr-547fa7a4048cbc2e.rlib,libarrow_cast-0b7117723b343c65.rlib,libatoi-c9a52adfe9dd2564.rlib,libryu-243c2c0ae3ed75b4.rlib,libbase64-1cab23258b68443b.rlib,liblexical_core-c2a41d0a6941285f.rlib,liblexical_write_float-9d65854ce5ab8f07.rlib,liblexical_write_integer-894216b914487c18.rlib,liblexical_parse_float-274078b1af50d567.rlib,liblexical_parse_integer-781bcb0a42285559.rlib,liblexical_util-4a71e416d58e0125.rlib,libstatic_assertions-4f12831487497211.rlib,libarrow_arith-00bcbf2ec2eb3322.rlib,libarrow_ord-fcdece9f7e87a9bf.rlib,libarrow_select-31b4c3cfa277427b.rlib,libarrow_array-c2dc23f827508dc6.rlib,libahash-d573f36c088b3179.rlib,libgetrandom-31b11224f8e2ea08.rlib,liblibc-045cef5bc264baa9.rlib,libonce_cell-83f4df333969eacb.rlib,libzerocopy-0db6330db7e4b762.rlib,libhashbrown-2c7527cd2fd4322d.rlib,libchrono-6d1bc7062186f166.rlib,libiana_time_zone-875b10f893e8f81d.rlib,libarrow_data-be090acb3cb83adb.rlib,libarrow_schema-25469a5878e8c886.rlib,libbitflags-2614952e3652d907.rlib,libarrow_buffer-8eb56dc26cbe25a3.rlib,libbytes-8b0f150f04d16150.rlib,libhalf-ed72603b54882276.rlib,libcfg_if-9dbfdc9eaf8f6a2d.rlib,libnum-436acb7880d5b290.rlib,libnum_iter-87f263003ea3e8dd.rlib,libnum_rational-d812b535c653cc6e.rlib,libnum_complex-c12c249f79450951.rlib,libnum_bigint-ff983ebd6646ce72.rlib,libnum_integer-f946a0e48063a631.rlib,libnum_traits-d0a5f363c632fb69.rlib}.rlib" "<sysroot>/lib/rustlib/aarch64-unknown-linux-gnu/lib/{libstd-*,libpanic_unwind-*,libobject-*,libmemchr-*,libaddr2line-*,libgimli-*,librustc_demangle-*,libstd_detect-*,libhashbrown-*,librustc_std_workspace_alloc-*,libminiz_oxide-*,libadler2-*,libunwind-*,libcfg_if-*,liblibc-*,liballoc-*,librustc_std_workspace_core-*,libcore-*,libcompiler_builtins-*}.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-L" "/tmp/rustc0jx15I/raw-dylibs" "-Wl,--eh-frame-hdr" "-Wl,-z,noexecstack" "-L" "<sysroot>/lib/rustlib/aarch64-unknown-linux-gnu/lib" "-o" "/arrow-rs/arrow-pyarrow-integration-testing/target/debug/deps/pyarrow-00909cd9e7866a35" "-Wl,--gc-sections" "-pie" "-Wl,-z,relro,-z,now" "-nodefaultlibs"
  = note: some arguments are omitted. use `--verbose` to show all linker arguments
  = note: /usr/bin/ld: /arrow-rs/arrow-pyarrow-integration-testing/target/debug/deps/libarrow_pyarrow-8b510eeadc952ad2.rlib(arrow_pyarrow-8b510eeadc952ad2.8xxa5xo5oql7wlj24034o033n.rcgu.o): in function `<pyo3::instance::Borrowed<pyo3::types::tuple::PyTuple> as pyo3::call::PyCallArgs>::call_positional':
          /root/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/pyo3-0.24.2/src/call.rs:213: undefined reference to `PyObject_Call'
```



# Are there any user-facing changes?

If there are user-facing changes then we may require documentation to be
updated before approving the PR.

If there are any breaking changes to public APIs, please call them out.

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: alamb

.github/workflows/integration.yml

@@ -165,8 +165,9 @@ jobs:
       - name: Run Rust tests
         run: |
           source venv/bin/activate
-          cargo test -p arrow-pyarrow
-      - name: Run tests
+          cd arrow-pyarrow-testing
+          cargo test
+      - name: Run Python tests
         run: |
           source venv/bin/activate
           cd arrow-pyarrow-integration-testing

.github/workflows/rust.yml

@@ -52,7 +52,7 @@ jobs:
           # do not produce debug symbols to keep memory usage down
           export RUSTFLAGS="-C debuginfo=0"
           # PyArrow tests happen in integration.yml.
-          cargo test --workspace --exclude arrow-pyarrow
+          cargo test --workspace
 
 
   # Check workspace wide compile and test with default features for
@@ -84,8 +84,7 @@ jobs:
           # do not produce debug symbols to keep memory usage down
           export RUSTFLAGS="-C debuginfo=0"
           export PATH=$PATH:/d/protoc/bin
-          # PyArrow tests happen in integration.yml.
-          cargo test --workspace --exclude arrow-pyarrow
+          cargo test --workspace 
 
 
   # Run cargo fmt for all crates

Cargo.toml

@@ -55,6 +55,9 @@ members = [
 resolver = "2"
 
 exclude = [
+    # arrow-pyarrow-testing is excluded because it requires a Python interpreter with the pyarrow package installed,
+    # which makes running `cargo test --all` fail if the appropriate Python environment is not set up.
+    "arrow-pyarrow-testing",
     # arrow-pyarrow-integration-testing is excluded because it requires different compilation flags, thereby
     # significantly changing how it is compiled within the workspace, causing the whole workspace to be compiled from
     # scratch this way, this is a stand-alone package that compiles independently of the others.

arrow-pyarrow-testing/Cargo.toml

@@ -0,0 +1,51 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+# Note this package is not published to crates.io, it is only used for testing
+# the arrow-pyarrow crate in the arrow-rs repository.
+#
+# It is not part of the workspace so that `cargo test --all` does not require
+# a Python interpreter or the pyarrow package to be installed.
+#
+# It is used to run tests that require a Python interpreter and the pyarrow
+# package installed. It is not intended to be used as a library or a standalone
+# application.
+#
+# It is different from `arrow-pyarrow-integration-testing` in that it works
+# with a standard pyarrow installation, rather than building a dynamic library
+# that can be loaded by Python (which requires additional configuraton of the
+# Python environment).
+
+[package]
+name = "arrow-pyarrow-testing"
+description = "Tests for arrow-pyarrow that require only a Python interpreter and pyarrow installed"
+version = "0.1.0"
+homepage = "https://github.com/apache/arrow-rs"
+repository = "https://github.com/apache/arrow-rs"
+authors = ["Apache Arrow <dev@arrow.apache.org>"]
+license = "Apache-2.0"
+keywords = [ "arrow" ]
+edition = "2021"
+rust-version = "1.81"
+publish = false
+
+
+[dependencies]
+# Note no dependency on arrow, to ensure arrow-pyarrow can be used by itself
+arrow-array = { path = "../arrow-array" }
+arrow-pyarrow = { path = "../arrow-pyarrow" }
+pyo3 = { version = "0.25", default-features = false }

arrow-pyarrow-testing/src/lib.rs

@@ -0,0 +1,20 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! This crate exists to provide a test environment for the `arrow-pyarrow` crate.
+//! It is not intended to be used by itself. See comments in Cargo.toml for more
+//! details.

arrow-pyarrow/tests/pyarrow.rs renamed to arrow-pyarrow-testing/tests/pyarrow.rs

@@ -15,6 +15,28 @@
 // specific language governing permissions and limitations
 // under the License.
 
+//! Tests pyarrow bindings
+//!
+//! This test requires installing the `pyarrow` python package. If you do not
+//! have this package installed, you will see an error such as the following:
+//!
+//! ```text
+//! PyErr { type: <class 'ModuleNotFoundError'>, value: ModuleNotFoundError("No module named 'pyarrow'"), traceback: None }
+//! ```
+//!
+//! # Notes
+//!
+//! You can not use a virtual environment to run these tests on MacOS, as it will
+//! fail to find the pyarrow module due to <https://github.com/PyO3/pyo3/issues/1741>
+//!
+//! One way to run them is to install the `pyarrow` package in the system Python,
+//! which might break other packages, so use with caution:
+//!
+//! ```shell
+//! brew install pipx
+//! pip3 install --break-system-packages pyarrow
+//! ```
+
 use arrow_array::builder::{BinaryViewBuilder, StringViewBuilder};
 use arrow_array::{
     Array, ArrayRef, BinaryViewArray, Int32Array, RecordBatch, StringArray, StringViewArray,