1 files changed, 61 insertions, 0 deletions
diff --git a/src/os/exec/internal_test.go b/src/os/exec/internal_test.go
new file mode 100644
index 0000000..68d517f
--- /dev/null
+++ b/src/os/exec/internal_test.go
@@ -0,0 +1,61 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package exec
+
+import (
+	"io"
+	"testing"
+)
+
+func TestPrefixSuffixSaver(t *testing.T) {
+	tests := []struct {
+		N      int
+		writes []string
+		want   string
+	}{
+		{
+			N:      2,
+			writes: nil,
+			want:   "",
+		},
+		{
+			N:      2,
+			writes: []string{"a"},
+			want:   "a",
+		},
+		{
+			N:      2,
+			writes: []string{"abc", "d"},
+			want:   "abcd",
+		},
+		{
+			N:      2,
+			writes: []string{"abc", "d", "e"},
+			want:   "ab\n... omitting 1 bytes ...\nde",
+		},
+		{
+			N:      2,
+			writes: []string{"ab______________________yz"},
+			want:   "ab\n... omitting 22 bytes ...\nyz",
+		},
+		{
+			N:      2,
+			writes: []string{"ab_______________________y", "z"},
+			want:   "ab\n... omitting 23 bytes ...\nyz",
+		},
+	}
+	for i, tt := range tests {
+		w := &prefixSuffixSaver{N: tt.N}
+		for _, s := range tt.writes {
+			n, err := io.WriteString(w, s)
+			if err != nil || n != len(s) {
+				t.Errorf("%d. WriteString(%q) = %v, %v; want %v, %v", i, s, n, err, len(s), nil)
+			}
+		}
+		if got := string(w.Bytes()); got != tt.want {
+			t.Errorf("%d. Bytes = %q; want %q", i, got, tt.want)
+		}
+	}
+}