Tracking: Overhauling the test suite

[dangotbanned]

Collecting together all of the various efforts going on 😳

Issues

• test: allow for tests to be run without Polars / PyArrow/ pandas installed #1726
• Skip tests for unavailable backends #2872
• test: ideas to speed up test suite #2818
• test: make constructor_with_tz and constructor_with_ns utilities #2742
• chore: test xfail unification #1893

Comments/Discord

• https://discord.com/channels/1235257048170762310/1402677544221937705
• test: allow for tests to be run without Polars / PyArrow/ pandas installed #1726 (comment)
• Skip tests for unavailable backends #2872 (comment)
• fix: Allow modin[pyarrow] to use more dtypes #2950 (comment)
• fix: Allow modin[pyarrow] to use more dtypes #2950 (review)
• fix(typing): Avoid overlapping DataFrame, LazyFrame #2944 (comment)
• feat: Add Expr.dt.offset_by() #2733 (comment)

Branches

• main...tests/run-with-no-deps
• main...testing-fixtures
• main...EdAbati:draft-new-constructor

Commits/Diffs/PRs

• https://github.com/narwhals-dev/narwhals/pull/2879/files#diff-9e08e8c7769db7b58089fd7659d75ca96df40bb7b5d50299d3a30abd54da9ad6
• https://github.com/narwhals-dev/narwhals/pull/2933/files#diff-9e08e8c7769db7b58089fd7659d75ca96df40bb7b5d50299d3a30abd54da9ad6
• https://github.com/narwhals-dev/narwhals/pull/2933/files#diff-e52e4ddd58b7ef887ab03c04116e676f6280b824ab7469d5d3080e5cba4f2128
• https://github.com/narwhals-dev/narwhals/pull/2933/files#diff-a1a637479cb57d5314c55a064184fda2df55e96627f3ef57da09b2c07e75b69f
• test: Branch time_unit for pandas nightly
• feat: Add assert_series_equal #2983
• test: Simplify read_scan_test, spark session #3024

Future

Besides something more ergonomic for us, we eventually want to spin off some tools into:

• [Enh]: Provide testing module to enable downstream libraries testing #739
• [Enh]: Testing module #2804

[dangotbanned]

@EdAbati @FBruzzesi
The PRs section only has diffs from my open PRs, feel free to add your own 🙌

[dangotbanned]

Hypothesis

Reading the hypothesis strategies docs was interesting.

There might be some stuff we can learn from how each of these work (in order of relevance to narwhals):

• strategies/array-api | source code
• strategies/pandas | source code
• strategies/numpy | source code