Remove the outputType parameter of collectOutput.

That information can be obtained from DataSet.Type.

flow/dataset_map_test.go

@@ -13,7 +13,7 @@ func TestMapSingleParameter(t *testing.T) {
 	}).Map(func(x, y int) int {
 		return x + y
 	})
-	got := collectOutput(dataset, reflect.TypeOf(int(1)))
+	got := collectOutput(dataset)
 
 	if want := []int{2, 4, 6}; !reflect.DeepEqual(got, want) {
 		t.Errorf("Got: %v want: %v", got, want)
@@ -29,7 +29,7 @@ func TestGroupByKeyMap(t *testing.T) {
 		return append([]int{key}, values...)
 	})
 
-	got := collectOutput(dataset, reflect.TypeOf([]int{}))
+	got := collectOutput(dataset)
 
 	if want := [][]int{{1, 2, 2}, {2, 4, 4}, {3, 6, 6}}; !reflect.DeepEqual(got, want) {
 		t.Errorf("Got %v want %v", got, want)
@@ -63,7 +63,7 @@ func TestCoGroupMap(t *testing.T) {
 		}
 	})
 
-	got := collectOutput(cogroupResult, reflect.TypeOf(result{}))
+	got := collectOutput(cogroupResult)
 	want := []result{
 		{
 			key:   1,

flow/dataset_output.go

@@ -85,18 +85,18 @@ func (d *Dataset) SaveTextToFile(fname string) {
 }
 
 // collectOutput collects the output of d and returns them as a slice of the
-// input type outputType.
+// type specified in d.Type.
 //
-// collectOutput intends to be used in tests. The implementation does not optimize
-// for performance or guarantee correctness under a wide range of use cases.
-func collectOutput(d *Dataset, outputType reflect.Type) interface{} {
-	outChan := reflect.MakeChan(reflect.ChanOf(reflect.BothDir, outputType), 0)
+// Intends to be used in tests. The implementation does not optimize for performance
+// or guarantee correctness under a wide range of use cases.
+func collectOutput(d *Dataset) interface{} {
+	outChan := reflect.MakeChan(reflect.ChanOf(reflect.BothDir, d.Type), 0)
 	d.AddOutput(outChan.Interface())
 
 	var wg sync.WaitGroup
 	wg.Add(1)
 
-	got := reflect.MakeSlice(reflect.SliceOf(outputType), 0, 1)
+	got := reflect.MakeSlice(reflect.SliceOf(d.Type), 0, 1)
 	go func() {
 		defer wg.Done()
 		for v, ok := outChan.Recv(); ok; v, ok = outChan.Recv() {

flow/dataset_output_test.go

@@ -13,7 +13,7 @@ func TestCollectOutput(t *testing.T) {
 		output <- "c"
 	}, 1)
 
-	got := collectOutput(dataset, reflect.TypeOf(""))
+	got := collectOutput(dataset)
 
 	if want := []string{"a", "b", "c"}; !reflect.DeepEqual(got, want) {
 		t.Errorf("Got %v want %v", got, want)