compress/flate: simplify the TestDegenerateHuffmanCoding data.

Change-Id: I223a4bd6e3ee31324b46ac79a4022e40f1868491
Reviewed-on: https://go-review.googlesource.com/8995
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/compress/flate/flate_test.go

@@ -10,8 +10,8 @@ package flate
 
 import (
 	"bytes"
-	"encoding/hex"
 	"io/ioutil"
+	"strings"
 	"testing"
 )
 
@@ -91,50 +91,28 @@ func TestInvalidBits(t *testing.T) {
 }
 
 func TestDegenerateHuffmanCoding(t *testing.T) {
-	// This test case is notable because:
-	//   1. It's decompressable by zlib.
-	//   2. It was generated by Go 1.4's compress/flate package.
-	//   3. It uses a degenerate dynamic Huffman coding block.
-	//
-	// The input is somewhat contrived though.  It's a sequence of
-	// 258 bytes with no 3+ byte sequence occuring more than once,
-	// except that the whole sequence is repeated twice.  This
-	// results in package flate emitting a single match token,
-	// which consequently means a single symbol in the distance
-	// coding table.
-	//
-	// Additionally, it uses very few unique byte values so that
-	// the overhead from storing the dynamic Huffman coding still
-	// results in a smaller encoding than using the fixed Huffman
-	// coding.
 	const (
-		originalHalf = "00013534215002452243512505010034133042401113" +
-			"400415101454022532410254513251155411055331124453555" +
-			"023120320201523334303524252551414033503012344230210" +
-			"310431305153005314321221315440455204052144332205422" +
-			"235434504441211420062622646656236416326065565261624" +
-			"6256136546"
-		compressedHex = "ecd081000030104251a5fad5f9a34d640a4f92b3144" +
-			"fa28366669a2ca54e542adba954cf7257c1422dd639ccde6a6b" +
-			"4b6cda659b885110f248d228a38ccd75954c91494b8415ab713" +
-			"42fd2e20683e3b5ea86aae13601ad40d6746a6bec221d07d7bb" +
-			"1db9fac2e9b61be7a3c7ceb9f5bec00b0000ffffecd08100003" +
-			"0104251a5fad5f9a34d640a4f92b3144fa28366669a2ca54e54" +
-			"2adba954cf7257c1422dd639ccde6a6b4b6cda659b885110f24" +
-			"8d228a38ccd75954c91494b8415ab71342fd2e20683e3b5ea86" +
-			"aae13601ad40d6746a6bec221d07d7bb1db9fac2e9b61be7a3c" +
-			"7ceb9f5bec00b0000ffff"
+		want = "abcabc"
+		// This compressed form has a dynamic Huffman block, even though a
+		// sensible encoder would use a literal data block, as the latter is
+		// shorter. Still, it is a valid flate compression of "abcabc". It has
+		// a degenerate Huffman table with only one coded value: the one
+		// non-literal back-ref copy of the first "abc" to the second "abc".
+		//
+		// To verify that this is decompressible with zlib (the C library),
+		// it's easy to use the Python wrapper library:
+		// >>> import zlib
+		// >>> compressed = "\x0c\xc2...etc...\xff\xff"
+		// >>> zlib.decompress(compressed, -15) # negative means no GZIP header.
+		// 'abcabc'
+		compressed = "\x0c\xc2\x01\x0d\x00\x00\x00\x82\xb0\xac\x4a\xff\x0e\xb0\x7d\x27" +
+			"\x06\x00\x00\xff\xff"
 	)
-
-	compressed, err := hex.DecodeString(compressedHex)
+	b, err := ioutil.ReadAll(NewReader(strings.NewReader(compressed)))
 	if err != nil {
 		t.Fatal(err)
 	}
-	data, err := ioutil.ReadAll(NewReader(bytes.NewReader(compressed)))
-	if err != nil {
-		t.Fatal(err)
-	}
-	if string(data) != originalHalf+originalHalf {
-		t.Fatal("Decompressed data does not match original")
+	if got := string(b); got != want {
+		t.Fatalf("got %q, want %q", got, want)
 	}
 }