wal: improve reader_test log

wal/reader_test.go

@@ -179,12 +179,16 @@ func TestReader(t *testing.T) {
 					if fields.HasValue("sync") {
 						require.NoError(t, f.Sync())
 					}
+
+					fmt.Fprintf(&buf, "%d..%d: write-garbage\n", offset, offset+int64(size))
 				case "corrupt-tail":
 					length := int64(fields.MustKeyValue("len").Int())
 					garbage := make([]byte, length)
 					rng.Read(garbage)
 					_, err := f.WriteAt(garbage, offset-length)
 					require.NoError(t, err)
+
+					fmt.Fprintf(&buf, "%d..%d: corrupt-tail\n", offset-length, offset)
 				default:
 					panic(fmt.Sprintf("unrecognized command %q", fields[0]))
 				}
@@ -206,7 +210,7 @@ func TestReader(t *testing.T) {
 			require.NoError(t, err)
 			log, ok := logs.Get(NumWAL(logNum))
 			if !ok {
-				return "not found"
+				return fmt.Sprintf("log with logNum %d not found", logNum)
 			}
 
 			segments := log.segments

wal/testdata/reader

@@ -181,7 +181,7 @@ r.NextRecord() = (rr, (000003-002.log: 2373), 2652 from previous files, EOF)
 
 read logNum=000004
 ----
-not found
+log with logNum 4 not found
 
 # Test a corrupted log file that encodes a record too small to be a valid batch.
 # The second "batch" only has a length of 5.
@@ -228,6 +228,7 @@ created "000005-001.log"
 0..55: batch #95499
 55..482: batch #95501
 482..692: batch #95506
+692..1045: write-garbage
 
 read logNum=000005
 ----
@@ -345,6 +346,7 @@ created "000007.log"
 55..482: batch #95501
 482..692: batch #95506
 692..46705: batch #95535
+45685..46705: corrupt-tail
 
 define logNum=000007 logNameIndex=001
 batch count=19 seq=95535 size=45991 sync