tests/basics: Add tests for assignment operator :=.

tests/basics/assign_expr.py

@@ -0,0 +1,29 @@
+(x := 4)
+print(x)
+
+if x := 2:
+    print(True)
+print(x)
+
+print(4, x := 5)
+print(x)
+
+x = 1
+print(x, x := 5, x)
+print(x)
+
+
+def foo():
+    print("any", any((hit := i) % 5 == 3 and (hit % 2) == 0 for i in range(10)))
+    return hit
+
+
+hit = 123
+print(foo())
+print(hit)  # shouldn't be changed by foo
+
+print("any", any((hit := i) % 5 == 3 and (hit % 2) == 0 for i in range(10)))
+print(hit)  # should be changed by above
+
+print([((m := k + 1), k * m) for k in range(4)])
+print(m)

tests/basics/assign_expr.py.exp

@@ -0,0 +1,14 @@
+4
+True
+2
+4 5
+5
+1 5 5
+5
+any True
+8
+123
+any True
+8
+[(1, 0), (2, 2), (3, 6), (4, 12)]
+4

tests/basics/assign_expr_syntaxerror.py

@@ -0,0 +1,16 @@
+# test SyntaxError with := operator
+
+def test(code):
+    try:
+        print(eval(code))
+    except SyntaxError:
+        print('SyntaxError')
+
+test("x := 1")
+test("((x, y) := 1)")
+
+# these are currently all allowed in MicroPython, but not in CPython
+test("([i := i + 1 for i in range(4)])")
+test("([i := -1 for i, j in [(1, 2)]])")
+test("([[(i := j) for i in range(2)] for j in range(2)])")
+test("([[(j := i) for i in range(2)] for j in range(2)])")

tests/basics/assign_expr_syntaxerror.py.exp

@@ -0,0 +1,6 @@
+SyntaxError
+SyntaxError
+[1, 2, 3, 4]
+[-1]
+[[0, 0], [1, 1]]
+[[0, 1], [0, 1]]