vis: refactored code to reflect using vis/unvis for file names

Added some more test cases for `vis`ing and `unvis`ing
strings, and a test case that walks/checks a directory with
filenames that require encoding. Had to change Path() to account
for possible errors Unvis() could return. Refactored Vis()/Unvis() into
go-mtree tar functionality as well.

Signed-off-by: Stephen Chung <schung@redhat.com>

vis_test.go

@@ -9,13 +9,17 @@ func TestVis(t *testing.T) {
 		{"[", "\\133"},
 		{" ", "\\040"},
 		{"	", "\\011"},
+		{"dir with space", "dir\\040with\\040space"},
+		{"consec   spaces", "consec\\040\\040\\040spaces"},
+		{"trailingsymbol[", "trailingsymbol\\133"},
+		{" [ leadingsymbols", "\\040\\133\\040leadingsymbols"},
+		{"no_need_for_encoding", "no_need_for_encoding"},
 	}
 
 	for i := range testset {
 		got, err := Vis(testset[i].Src)
 		if err != nil {
 			t.Errorf("working with %q: %s", testset[i].Src, err)
-			continue
 		}
 		if got != testset[i].Dest {
 			t.Errorf("expected %#v; got %#v", testset[i].Dest, got)
@@ -33,3 +37,13 @@ func TestVis(t *testing.T) {
 		}
 	}
 }
+
+// The resulting string of Vis output could potentially be four times longer than
+// the original. Vis must handle this possibility.
+func TestVisLength(t *testing.T) {
+	testString := "All work and no play makes Jack a dull boy\n"
+	for i := 0; i < 20; i++ {
+		Vis(testString)
+		testString = testString + testString
+	}
+}