Add test for VMC ground state search

Test/GroundState/test_groundstate.py

@@ -0,0 +1,42 @@
+from pytest import approx
+import netket as nk
+from mpi4py import MPI
+
+
+SEED = 3141592
+
+
+def test_vmc_iterator():
+    g = nk.graph.Hypercube(length=8, n_dim=1)
+    hi = nk.hilbert.Spin(s=0.5, graph=g)
+
+    ma = nk.machine.RbmSpin(hilbert=hi, alpha=1)
+    ma.init_random_parameters(seed=SEED, sigma=0.01)
+
+    ha = nk.operator.Ising(hi, h=1.0)
+    sa = nk.sampler.MetropolisLocal(machine=ma)
+    sa.seed(SEED)
+    op = nk.optimizer.Sgd(learning_rate=0.1)
+
+    vmc = nk.gs.vmc.Vmc(
+        hamiltonian=ha,
+        sampler=sa,
+        optimizer=op,
+        n_samples=500,
+        diag_shift=0.01)
+
+    count = 0
+    last_step = None
+    for i, step in enumerate(vmc.iter(300, store_params=False)):
+        assert i == step.current_step
+        count += 1
+        obs = step.observables
+        assert len(obs) == 2
+        for name in 'Energy', 'EnergyVariance':
+            assert name in obs
+            e = obs[name]
+            assert 'Mean' in e and 'Sigma' in e and 'Taucorr' in e
+        last_step = step
+
+    assert count == 300
+    assert last_step.observables.Energy['Mean'] == approx(-10.25, abs=0.2)