How to save all console output to file in R?

I want to redirect all console text to a file. Here is what I tried:

> sink("test.log", type=c("output", "message"))
> a <- "a"
> a
> How come I do not see this in log
Error: unexpected symbol in "How come"

Here is what I got in test.log:

[1] "a"

Here is what I want in test.log:

> a <- "a"
> a
[1] "a"
> How come I do not see this in log
Error: unexpected symbol in "How come"

What am I doing wrong? Thanks!