parser/gotest: Create LimitedLineReader

parser/gotest/internal/reader/reader_test.go

@@ -0,0 +1,68 @@
+package reader
+
+import (
+	"bufio"
+	"io"
+	"strings"
+	"testing"
+)
+
+const testingLimit = 4 * 1024 * 1024
+
+func TestLimitedLineReader(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", testingLimit - 1},
+		{"at limit", testingLimit},
+		{"just over limit", testingLimit + 1},
+		{"over limit", testingLimit + 128},
+	}
+
+	for _, test := range tests {
+		t.Run(test.desc, func(t *testing.T) {
+			line1 := string(make([]byte, test.inputSize))
+			line2 := "other line"
+			input := strings.NewReader(strings.Join([]string{line1, line2}, "\n"))
+			r := NewLimitedLineReader(input, testingLimit)
+
+			got, err := r.ReadLine()
+			if err != nil {
+				t.Fatalf("ReadLine() returned error %v", err)
+			}
+
+			want := line1
+			if len(line1) > testingLimit {
+				want = want[:testingLimit]
+			}
+			if got != want {
+				t.Fatalf("ReadLine() returned incorrect line, got len %d want len %d", len(got), len(want))
+			}
+
+			got, err = r.ReadLine()
+			if err != nil {
+				t.Fatalf("ReadLine() returned error %v", err)
+			}
+			want = line2
+			if got != want {
+				t.Fatalf("ReadLine() returned incorrect line, got len %d want len %d", len(got), len(want))
+			}
+
+			got, err = r.ReadLine()
+			if err != io.EOF {
+				t.Fatalf("ReadLine() returned unexpected error, got %v want %v\n", err, io.EOF)
+			}
+			if got != "" {
+				t.Fatalf("ReadLine() returned unexpected line, got %v want nothing\n", got)
+			}
+		})
+	}
+}