test: add coverage for streaming fallback and maybe_group_terms_polars

Author: FBumann

test/test_common.py

@@ -23,6 +23,7 @@
     get_dims_with_index_levels,
     is_constant,
     iterate_slices,
+    maybe_group_terms_polars,
 )
 from linopy.testing import assert_linequal, assert_varequal
 
@@ -737,3 +738,20 @@ def test_is_constant() -> None:
     ]
     for cv in constant_values:
         assert is_constant(cv)
+
+
+def test_maybe_group_terms_polars_no_duplicates():
+    """Fast path: distinct (labels, vars) pairs skip group_by."""
+    df = pl.DataFrame({"labels": [0, 0], "vars": [1, 2], "coeffs": [3.0, 4.0]})
+    result = maybe_group_terms_polars(df)
+    assert result.shape == (2, 3)
+    assert result.columns == ["labels", "vars", "coeffs"]
+    assert result["coeffs"].to_list() == [3.0, 4.0]
+
+
+def test_maybe_group_terms_polars_with_duplicates():
+    """Slow path: duplicate (labels, vars) pairs trigger group_by."""
+    df = pl.DataFrame({"labels": [0, 0], "vars": [1, 1], "coeffs": [3.0, 4.0]})
+    result = maybe_group_terms_polars(df)
+    assert result.shape == (1, 3)
+    assert result["coeffs"].to_list() == [7.0]

test/test_io.py

@@ -7,6 +7,7 @@
 
 import pickle
 from pathlib import Path
+from unittest.mock import patch
 
 import numpy as np
 import pandas as pd
@@ -15,7 +16,7 @@
 import xarray as xr
 
 from linopy import LESS_EQUAL, Model, available_solvers, read_netcdf
-from linopy.io import signed_number
+from linopy.io import _format_and_write, signed_number
 from linopy.testing import assert_model_equal
 
 
@@ -336,3 +337,48 @@ def test_to_file_lp_with_negative_zero_coefficients(tmp_path: Path) -> None:
 
     # Verify Gurobi can read it without errors
     gurobipy.read(str(fn))
+
+
+def test_format_and_write_streaming_fallback(tmp_path):
+    """Test that _format_and_write falls back to eager when streaming fails."""
+    df = pl.DataFrame({"a": ["x", "y"], "b": ["1", "2"]})
+    columns = [pl.col("a"), pl.lit(" "), pl.col("b")]
+
+    # Normal path
+    fn1 = tmp_path / "normal.lp"
+    with open(fn1, "wb") as f:
+        _format_and_write(df, columns, f)
+    content_normal = fn1.read_text()
+
+    # Force streaming to fail
+    original_collect = pl.LazyFrame.collect
+
+    def failing_collect(self, *args, **kwargs):
+        if kwargs.get("engine") == "streaming":
+            raise RuntimeError("simulated streaming failure")
+        return original_collect(self, *args, **kwargs)
+
+    fn2 = tmp_path / "fallback.lp"
+    with patch.object(pl.LazyFrame, "collect", failing_collect):
+        with open(fn2, "wb") as f:
+            _format_and_write(df, columns, f)
+    content_fallback = fn2.read_text()
+
+    assert content_normal == content_fallback
+
+
+def test_to_file_lp_same_sign_constraints(tmp_path):
+    """Test LP writing when all constraints have the same sign operator."""
+    m = Model()
+    N = np.arange(5)
+    x = m.add_variables(coords=[N], name="x")
+    # All constraints use <=
+    m.add_constraints(x <= 10, name="upper")
+    m.add_constraints(x <= 20, name="upper2")
+    m.add_objective(x.sum())
+
+    fn = tmp_path / "same_sign.lp"
+    m.to_file(fn)
+    content = fn.read_text()
+    assert "s.t." in content
+    assert "<=" in content