We cannot compare two Func arguments to check if they are equal using
the reflect package. This leads to the following misleading panic:
```go
handler := func(http.ResponseWriter, *http.Request) {}
muxMock.On("HandleFunc", "/", handler)
muxMock.HandleFunc("/", handler)
// panics arguing handler != handler
```
Since we cannot fix this behaviour using reflection, this patch
provides a better panic with a meaningful workaround.
```go
handler := func(http.ResponseWriter, *http.Request) {}
muxMock.On("HandleFunc", "/", handler)
// panics recommending defining the expectatin with:
// AnythingOfType("func(http.ResponseWriter, *http.Request)")
```
Solution following the panic's instructions:
```go
handler := func(http.ResponseWriter, *http.Request) {}
muxMock.On("HandleFunc", "/",
mock.AnythingOfType("func(http.ResponseWriter, *http.Request)"))
muxMock.HandleFunc("/", handler)
```
Some methods in Go take a pointer to a struct or a map and are supposed
to set some values in the referenced argument. Using Return is not
enough to mock such methods.
We are introducing a Run method that allows setting a Call handler to
make your mock update such referenced values.
Example usage mocking a service that finds a user in a data store and
fills the values in the provided struct:
```go
m.On("Find", 1, mock.AnythingOfType(*User))
.Return(nil)
.Run(func(args mock.Arguments) {
u := args.Get(0).(*User)
u.ID = 1
u.Email = "mail@example.com"
})
```
You sometimes want to test concurrent behaviour like timeouts, but it
was not currently possible with our mocks.
This commits adds the following functions to Mock:
`After` will block m.Called for the given duration before returning.
```golang
func (m *Mock) After(d time.Duration) *Mock
Mock.On("MyMethod", arg1).After(1 * time.Millisecond)
```
`WaitUntil` is the primitive under `After`, and it's exposed in case you
want somebody wants more control over the returns. `Called` blocks until the w
channel is closed or receives a message.
```golang
func (m *Mock) WaitUntil(w <-chan time.Time) *Mock
Mock.On("MyMethod", arg1).WaitUntil(time.After(1 * time.Millisecond))
```
