Add Tests for Bytes Concat

Author: colinxu2020

mypyc/test-data/irbuild-bytes.test

@@ -299,3 +299,26 @@ def foo(b: bytes, ba: bytearray) -> None:
 [out]
 main:7: error: Argument 1 to "bytes_func" has incompatible type "bytearray"; expected "bytes"
 main:8: error: Argument 1 to "bytearray_func" has incompatible type "bytes"; expected "bytearray"
+
+[case testBytesConcatRefcount]
+def f(a: bytes, b: bytes) -> bytes:
+    return b"1" + b
+[out]
+def f(a, b):
+    a, b, r0, r1 :: bytes
+L0:
+    r0 = b'1'
+    r1 = CPyBytes_Concat(r0, b)
+    return r1
+
+[case testChainedBytesConcatRefcount]
+def f(a: bytes, b: bytes, c: bytes) -> bytes:
+    return b"1" + b + c
+[out]
+def f(a, b, c):
+    a, b, c, r0, r1, r2 :: bytes
+L0:
+    r0 = b'1'
+    r1 = CPyBytes_Concat(r0, b)
+    r2 = CPyBytes_Concat(r1, c)
+    return r2