Function TestWriterReadFromCounts

pkg/bufio/bufio_test.go:587–630

TestWriterReadFromCounts tests that using io.Copy to copy into a bufio.Writer does not prematurely flush the buffer. For example, when buffering writes to a network socket, excessive network writes should be avoided.

(t *testing.T)

// buffering writes to a network socket, excessive network writes should be
// avoided.
func TestWriterReadFromCounts(t *testing.T) {
	var w0 writeCountingDiscard
	b0 := NewWriterSize(&w0, 1234)
	_, _ = b0.WriteString(strings.Repeat("x", 1000))
	if w0 != 0 {
		t.Fatalf("write 1000 'x's: got %d writes, want 0", w0)
	}
	_, _ = b0.WriteString(strings.Repeat("x", 200))
	if w0 != 0 {
		t.Fatalf("write 1200 'x's: got %d writes, want 0", w0)
	}
	_, _ = io.Copy(b0, onlyReader{strings.NewReader(strings.Repeat("x", 30))})
	if w0 != 0 {
		t.Fatalf("write 1230 'x's: got %d writes, want 0", w0)
	}
	_, _ = io.Copy(b0, onlyReader{strings.NewReader(strings.Repeat("x", 9))})
	if w0 != 1 {
		t.Fatalf("write 1239 'x's: got %d writes, want 1", w0)
	}

	var w1 writeCountingDiscard
	b1 := NewWriterSize(&w1, 1234)
	_, _ = b1.WriteString(strings.Repeat("x", 1200))
	_ = b1.Flush()
	if w1 != 1 {
		t.Fatalf("flush 1200 'x's: got %d writes, want 1", w1)
	}
	_, _ = b1.WriteString(strings.Repeat("x", 89))
	if w1 != 1 {
		t.Fatalf("write 1200 + 89 'x's: got %d writes, want 1", w1)
	}
	_, _ = io.Copy(b1, onlyReader{strings.NewReader(strings.Repeat("x", 700))})
	if w1 != 1 {
		t.Fatalf("write 1200 + 789 'x's: got %d writes, want 1", w1)
	}
	_, _ = io.Copy(b1, onlyReader{strings.NewReader(strings.Repeat("x", 600))})
	if w1 != 2 {
		t.Fatalf("write 1200 + 1389 'x's: got %d writes, want 2", w1)
	}
	_ = b1.Flush()
	if w1 != 3 {
		t.Fatalf("flush 1200 + 1389 'x's: got %d writes, want 3", w1)
	}
}

// A writeCountingDiscard is like ioutil.Discard and counts the number of times
// Write is called on it.