test: add tests for rewrite_fasta

Adds tests/tools/test_rewrite_fasta.py covering rewrite_fasta() using
pytest's tmp_path fixture:
- Canonical autosomes (chr1, chr22) are kept
- Sex chromosomes (chrX, chrY) and chrMT are kept
- Alt contigs (chr1_alt) and decoys (chrUn_gl000220, chrEBV) are filtered
- Mixed input with canonical and non-canonical contigs interleaved
- Empty input produces empty output
- Multi-line sequences are written in full

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ameynert

divref/tests/tools/test_rewrite_fasta.py

@@ -0,0 +1,53 @@
+"""Tests for the rewrite_fasta tool."""
+
+from pathlib import Path
+
+from divref.tools.rewrite_fasta import rewrite_fasta
+
+
+def _write_fasta(path: Path, contigs: list[tuple[str, str]]) -> None:
+    with open(path, "w") as f:
+        for name, seq in contigs:
+            f.write(f">{name}\n{seq}\n")
+
+
+def test_keeps_canonical_autosomes(tmp_path: Path) -> None:
+    _write_fasta(tmp_path / "in.fa", [("chr1", "ACGT"), ("chr22", "TTTT")])
+    rewrite_fasta(fasta_path=tmp_path / "in.fa", output_path=tmp_path / "out.fa")
+    assert (tmp_path / "out.fa").read_text() == ">chr1\nACGT\n>chr22\nTTTT\n"
+
+
+def test_keeps_sex_and_mt_chromosomes(tmp_path: Path) -> None:
+    _write_fasta(tmp_path / "in.fa", [("chrX", "AAAA"), ("chrY", "CCCC"), ("chrMT", "GGGG")])
+    rewrite_fasta(fasta_path=tmp_path / "in.fa", output_path=tmp_path / "out.fa")
+    assert (tmp_path / "out.fa").read_text() == ">chrX\nAAAA\n>chrY\nCCCC\n>chrMT\nGGGG\n"
+
+
+def test_filters_non_canonical(tmp_path: Path) -> None:
+    _write_fasta(
+        tmp_path / "in.fa",
+        [("chr1", "ACGT"), ("chr1_alt", "AAAA"), ("chrUn_gl000220", "TTTT")],
+    )
+    rewrite_fasta(fasta_path=tmp_path / "in.fa", output_path=tmp_path / "out.fa")
+    assert (tmp_path / "out.fa").read_text() == ">chr1\nACGT\n"
+
+
+def test_mixed_canonical_and_non_canonical(tmp_path: Path) -> None:
+    _write_fasta(
+        tmp_path / "in.fa",
+        [("chr1", "ACGT"), ("chr1_alt", "AAAA"), ("chr2", "TTTT"), ("chrEBV", "CCCC")],
+    )
+    rewrite_fasta(fasta_path=tmp_path / "in.fa", output_path=tmp_path / "out.fa")
+    assert (tmp_path / "out.fa").read_text() == ">chr1\nACGT\n>chr2\nTTTT\n"
+
+
+def test_empty_fasta(tmp_path: Path) -> None:
+    (tmp_path / "in.fa").write_text("")
+    rewrite_fasta(fasta_path=tmp_path / "in.fa", output_path=tmp_path / "out.fa")
+    assert (tmp_path / "out.fa").read_text() == ""
+
+
+def test_multiline_sequence_preserved(tmp_path: Path) -> None:
+    (tmp_path / "in.fa").write_text(">chr1\nACGT\nTGCA\n>chr1_alt\nAAAA\n")
+    rewrite_fasta(fasta_path=tmp_path / "in.fa", output_path=tmp_path / "out.fa")
+    assert (tmp_path / "out.fa").read_text() == ">chr1\nACGT\nTGCA\n"