parser/gotest: Add support for parsing lines longer than 64K

The gotest parser used a bufio.Scanner to read its input, which
prevented us from reading lines larger than 64K.

In order to support reading larger lines, bufio.Scanner has been
replaced with bufio.Reader. The maximum line size has been increased to
4MiB and instead of returning an error when reading lines that exceed
the maximum size, we truncate that line and continue parsing.

Fixes #135

parser/gotest/gotest_test.go

@@ -1,6 +1,8 @@
 package gotest
 
 import (
+	"bufio"
+	"bytes"
 	"fmt"
 	"strings"
 	"testing"
@@ -216,6 +218,58 @@ func TestParseLine(t *testing.T) {
 	}
 }
 
+func TestParseLargeLine(t *testing.T) {
+	tests := []struct {
+		desc      string
+		inputSize int
+	}{
+		{"small size", 128},
+		{"under buf size", 4095},
+		{"buf size", 4096},
+		{"multiple of buf size ", 4096 * 2},
+		{"not multiple of buf size", 10 * 1024},
+		{"bufio.MaxScanTokenSize", bufio.MaxScanTokenSize},
+		{"over bufio.MaxScanTokenSize", bufio.MaxScanTokenSize + 1},
+		{"under limit", maxLineSize - 1},
+		{"at limit", maxLineSize},
+		{"just over limit", maxLineSize + 1},
+		{"over limit", maxLineSize + 128},
+	}
+
+	createInput := func(lines ...string) *bytes.Buffer {
+		buf := &bytes.Buffer{}
+		buf.WriteString("=== RUN TestOne\n--- PASS: TestOne (0.00s)\n")
+		buf.WriteString(strings.Join(lines, "\n"))
+		return buf
+	}
+
+	for _, test := range tests {
+		t.Run(test.desc, func(t *testing.T) {
+			line1 := string(make([]byte, test.inputSize))
+			line2 := "other line"
+			report, err := NewParser().Parse(createInput(line1, line2))
+			if err != nil {
+				t.Fatalf("Parse() returned error %v", err)
+			} else if len(report.Packages) != 1 {
+				t.Fatalf("Parse() returned unexpected number of packages, got %d want 1.", len(report.Packages))
+			} else if len(report.Packages[0].Output) != 2 {
+				t.Fatalf("Parse() returned unexpected number of output lines, got %d want 1.", len(report.Packages[0].Output))
+			}
+
+			want := line1
+			if len(want) > maxLineSize {
+				want = want[:maxLineSize]
+			}
+			if got := report.Packages[0].Output[0]; got != want {
+				t.Fatalf("Parse() output line1 mismatch, got len %d want len %d", len(got), len(want))
+			}
+			if report.Packages[0].Output[1] != line2 {
+				t.Fatalf("Parse() output line2 mismatch, got %v want %v", report.Packages[0].Output[1], line2)
+			}
+		})
+	}
+}
+
 func TestReport(t *testing.T) {
 	events := []Event{
 		{Type: "run_test", Name: "TestOne"},