Add tests for multiple assignments and unpacking

tests/syntax/test_assignments.py

@@ -0,0 +1,66 @@
+# Minimal semantics tests for multiple assignment and LHS unpacking.
+
+import pytest
+
+from tests.utils import compileScenic, sampleEgoActions
+
+
+def test_multiple_assignment_swap():
+    scenario = compileScenic(
+        """
+        behavior Foo():
+            a = 1
+            b = 2
+            a, b = b, a
+            take a
+            take b
+        ego = new Object with behavior Foo
+        """
+    )
+    actions = sampleEgoActions(scenario, maxSteps=2)
+    assert actions == [2, 1]
+
+
+def test_lhs_tuple_unpack():
+    scenario = compileScenic(
+        """
+        behavior Foo():
+            x, y = (3, 4)
+            take x
+            take y
+        ego = new Object with behavior Foo
+        """
+    )
+    assert sampleEgoActions(scenario, maxSteps=2) == [3, 4]
+
+
+def test_unpack_from_distribution_pair():
+    scenario = compileScenic(
+        """
+        behavior Foo():
+            pair = Uniform((0, 1), (1, 0))
+            x, y = pair
+            take x
+            take y
+        ego = new Object with behavior Foo
+        """
+    )
+    outs = [tuple(sampleEgoActions(scenario, maxSteps=2)) for _ in range(60)]
+    assert {(0, 1), (1, 0)} <= set(outs)
+
+
+@pytest.mark.parametrize(
+    "rhs",
+    ["(1, 2, 3)", "(1,)"],  # too many; not enough
+)
+def test_unpack_arity_mismatch_exec_raises(rhs):
+    scenario = compileScenic(
+        f"""
+        behavior Foo():
+            x, y = {rhs}
+            take x
+        ego = new Object with behavior Foo
+    """
+    )
+    with pytest.raises(ValueError):
+        sampleEgoActions(scenario, maxSteps=1)

tests/syntax/test_parser.py

@@ -168,6 +168,20 @@ def test_workspace_assign(self):
                 assert False
 
 
+class TestAssign:
+    def test_tuple_lhs_parses(self):
+        mod = parse_string_helper("a, b = 1, 2")
+        stmt = mod.body[0]
+        match stmt:
+            case Assign(
+                targets=[Tuple([Name("a"), Name("b")])],
+                value=Tuple([Constant(1), Constant(2)]),
+            ):
+                assert True
+            case _:
+                assert False
+
+
 class TestInitialScenario:
     def test_initial_scenario(self):
         mod = parse_string_helper("initial scenario")