TST: added from_grid unit tests to cover constructor-level validation and the explicit API.

Author: aZira371

tests/unit/mathutils/test_function_from_grid.py

@@ -0,0 +1,37 @@
+import numpy as np
+import pytest
+
+from rocketpy.mathutils.function import Function
+
+
+def test_from_grid_unsupported_extrapolation_raises():
+    """from_grid should reject unsupported extrapolation names with ValueError."""
+    mach = np.array([0.0, 1.0])
+    reynolds = np.array([1e5, 2e5])
+    grid = np.zeros((mach.size, reynolds.size))
+
+    with pytest.raises(ValueError):
+        Function.from_grid(grid, [mach, reynolds], extrapolation="unsupported_mode")
+
+
+def test_from_grid_is_multidimensional_property():
+    """Ensure `is_multidimensional` is True for ND grid Functions and False for 1D."""
+    mach = np.array([0.0, 0.5, 1.0])
+    reynolds = np.array([1e5, 2e5, 3e5])
+    alpha = np.array([0.0, 2.0])
+
+    M, R, A = np.meshgrid(mach, reynolds, alpha, indexing="ij")
+    cd_data = 0.1 + 0.2 * M + 1e-7 * R + 0.01 * A
+
+    func_nd = Function.from_grid(
+        cd_data, [mach, reynolds, alpha], inputs=["Mach", "Reynolds", "Alpha"], outputs="Cd"
+    )
+
+    assert hasattr(func_nd, "is_multidimensional")
+    assert func_nd.is_multidimensional is True
+
+    # 1D Function constructed from a two-column array should not be multidimensional
+    src = np.column_stack((mach, 0.5 + 0.1 * mach))
+    func_1d = Function(src, inputs=["Mach"], outputs="Cd")
+    assert hasattr(func_1d, "is_multidimensional")
+    assert func_1d.is_multidimensional is False