test: Copy convolution test for fk table from grid one

pineappl_py/tests/test_fk_table.py

@@ -0,0 +1,40 @@
+import numpy as np
+
+import pineappl
+
+
+class TestFkTable:
+    def fake_grid(self, bins=None):
+        lumis = [pineappl.lumi.LumiEntry([(1, 21, 0.1)])]
+        orders = [pineappl.grid.Order(3, 0, 0, 0)]
+        bin_limits = np.array([1e-7, 1e-3, 1] if bins is None else bins, dtype=float)
+        subgrid_params = pineappl.subgrid.SubgridParams()
+        g = pineappl.grid.Grid.create(lumis, orders, bin_limits, subgrid_params)
+        return g
+
+    def test_convolute_with_one(self):
+        g = self.fake_grid()
+
+        # DIS grid
+        xs = np.linspace(0.5, 1.0, 5)
+        vs = xs.copy()
+        subgrid = pineappl.import_only_subgrid.ImportOnlySubgridV1(
+            vs[np.newaxis, :, np.newaxis],
+            np.array([90.0]),
+            xs,
+            np.array([1.0]),
+        )
+        g.set_subgrid(0, 0, 0, subgrid)
+        fk = pineappl.fk_table.FkTable(g)
+        np.testing.assert_allclose(
+            fk.convolute_with_one(2212, lambda pid, x, q2: 0.0, lambda q2: 0.0),
+            [0.0] * 2,
+        )
+        np.testing.assert_allclose(
+            fk.convolute_with_one(2212, lambda pid, x, q2: 1, lambda q2: 1.0),
+            [5e6 / 9999, 0.0],
+        )
+        np.testing.assert_allclose(
+            fk.convolute_with_one(2212, lambda pid, x, q2: 1, lambda q2: 2.0),
+            [2**3 * 5e6 / 9999, 0.0],
+        )