bpo-32630: Use contextvars in decimal (GH-5278)

Lib/test/test_asyncio/test_context.py

@@ -0,0 +1,29 @@
+import asyncio
+import decimal
+import unittest
+
+
+class DecimalContextTest(unittest.TestCase):
+
+    def test_asyncio_task_decimal_context(self):
+        async def fractions(t, precision, x, y):
+            with decimal.localcontext() as ctx:
+                ctx.prec = precision
+                a = decimal.Decimal(x) / decimal.Decimal(y)
+                await asyncio.sleep(t)
+                b = decimal.Decimal(x) / decimal.Decimal(y ** 2)
+                return a, b
+
+        async def main():
+            r1, r2 = await asyncio.gather(
+                fractions(0.1, 3, 1, 3), fractions(0.2, 6, 1, 3))
+
+            return r1, r2
+
+        r1, r2 = asyncio.run(main())
+
+        self.assertEqual(str(r1[0]), '0.333')
+        self.assertEqual(str(r1[1]), '0.111')
+
+        self.assertEqual(str(r2[0]), '0.333333')
+        self.assertEqual(str(r2[1]), '0.111111')