Add T.Skip(count int, description string)

The spec [1] suggests "ok 23 # SKIP ...", but if you attempt this with:

  t.Pass("# SKIP foo")

you get an extra hyphen ("ok 23 - # SKIP foo") which is parsed as a
successful test (and not a skipped test).

Michael gives the following example to motivate 'count' [2]:

  if ConditionIsMet() {
    t.Ok(Foo(), "foo")
    t.Ok(Bar(), "bar")
  } else {
    t.Skip(2, "condition not met")
  }

The spec example of this is in [3], showing no special syntax for
skipping multiple tests (although there is a special syntax for
skipping *all* the tests).

Also alphabetize TESTS in the Makefile.

[1]: http://testanything.org/tap-version-13-specification.html#skipping-tests
[2]: mndrix/tap-go#6 (comment)
[3]: http://testanything.org/tap-version-13-specification.html#skipping-a-few

Author: wking

util/tap/Makefile

@@ -1,4 +1,4 @@
-TESTS = auto check diagnostic known failing writer
+TESTS = auto check diagnostic failing known skip writer
 GOPATH = $(CURDIR)/gopath
 
 .PHONY: $(TESTS)

util/tap/tap.go

@@ -117,6 +117,14 @@ func escapeNewlines(s string) string {
 	return strings.Replace(strings.TrimRight(s, "\n"), "\n", "\n# ", -1)
 }
 
+// Skip indicates that a test has been skipped.
+func (t *T) Skip(count int, description string) {
+	for i := 0; i < count; i++ {
+		t.printf("ok %d # SKIP %s\n", t.nextTestNumber, description)
+		t.nextTestNumber++
+	}
+}
+
 // Diagnostic generates a diagnostic from the message,
 // which may span multiple lines.
 func (t *T) Diagnostic(message string) {

util/tap/test/skip/main.go

@@ -0,0 +1,30 @@
+package main
+
+import (
+	"bytes"
+	"io"
+	"os"
+
+	tap "github.com/mndrix/tap-go"
+)
+
+func main() {
+	// collect output for comparison later
+	buf := new(bytes.Buffer)
+	t := tap.New()
+	t.Writer = io.MultiWriter(os.Stdout, buf)
+
+	t.Header(4)
+	t.Skip(1, "insufficient flogiston pressure")
+	t.Skip(2, "no /sys directory")
+
+	got := buf.String()
+	t.Ok(got == expected, "skip gave expected output")
+}
+
+const expected = `TAP version 13
+1..4
+ok 1 # SKIP insufficient flogiston pressure
+ok 2 # SKIP no /sys directory
+ok 3 # SKIP no /sys directory
+`