Add tests for LineReader

Author: mrnugget

diff/reader_util.go

@@ -3,9 +3,12 @@ package diff
 import (
 	"bufio"
 	"bytes"
+	"errors"
 	"io"
 )
 
+var ErrLineReaderUninitialized = errors.New("line reader not initialized")
+
 func newLineReader(r io.Reader) *lineReader {
 	return &lineReader{reader: bufio.NewReader(r)}
 }
@@ -43,6 +46,10 @@ func (l *lineReader) readLine() ([]byte, error) {
 // io.EOF and bufio.ErrBufferFull errors are ignored so that the function can
 // be used when at the end of the file.
 func (l *lineReader) nextLineStartsWith(prefix string) (bool, error) {
+	if l.cachedNextLine == nil && l.cachedNextLineErr == nil {
+		l.cachedNextLine, l.cachedNextLineErr = readLine(l.reader)
+	}
+
 	return l.lineHasPrefix(l.cachedNextLine, prefix, l.cachedNextLineErr)
 }
 
@@ -51,7 +58,15 @@ func (l *lineReader) nextLineStartsWith(prefix string) (bool, error) {
 //
 // io.EOF and bufio.ErrBufferFull errors are ignored so that the function can
 // be used when at the end of the file.
+//
+// The lineReader MUST be initialized by calling readLine at least once before
+// calling nextLineStartsWith. Otherwise ErrLineReaderUninitialized will be
+// returned.
 func (l *lineReader) nextNextLineStartsWith(prefix string) (bool, error) {
+	if l.cachedNextLine == nil && l.cachedNextLineErr == nil {
+		l.cachedNextLine, l.cachedNextLineErr = readLine(l.reader)
+	}
+
 	next, err := l.reader.Peek(len(prefix))
 	return l.lineHasPrefix(next, prefix, err)
 }

diff/reader_util_test.go

@@ -66,3 +66,167 @@ index 0000000..3be2928`,
 		})
 	}
 }
+
+func TestLineReader_ReadLine(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  []string
+	}{
+		{
+			name:  "empty",
+			input: "",
+			want:  []string{},
+		},
+		{
+			name:  "single_line",
+			input: "@@ -0,0 +1,62 @@",
+			want:  []string{"@@ -0,0 +1,62 @@"},
+		},
+		{
+			name:  "single_lf_terminated_line",
+			input: "@@ -0,0 +1,62 @@\n",
+			want:  []string{"@@ -0,0 +1,62 @@"},
+		},
+		{
+			name:  "single_crlf_terminated_line",
+			input: "@@ -0,0 +1,62 @@\r\n",
+			want:  []string{"@@ -0,0 +1,62 @@"},
+		},
+		{
+			name: "multi_line",
+			input: `diff --git a/test.go b/test.go
+new file mode 100644
+index 0000000..3be2928`,
+			want: []string{
+				"diff --git a/test.go b/test.go",
+				"new file mode 100644",
+				"index 0000000..3be2928",
+			},
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			in := newLineReader(strings.NewReader(test.input))
+			out := []string{}
+			for {
+				l, err := in.readLine()
+				if err == io.EOF {
+					break
+				}
+				if err != nil {
+					t.Fatal(err)
+				}
+				out = append(out, string(l))
+			}
+			if !reflect.DeepEqual(test.want, out) {
+				t.Errorf("read lines not equal: want %v, got %v", test.want, out)
+			}
+		})
+	}
+}
+
+func TestLineReader_NextLineStartsWith(t *testing.T) {
+	input := `aaa rest of line
+bbbrest of line
+ccc rest of line`
+
+	in := newLineReader(strings.NewReader(input))
+
+	type assertion struct {
+		prefix string
+		want   bool
+	}
+
+	testsPerReadLine := []struct {
+		nextLine        []assertion
+		nextNextLine    []assertion
+		wantReadLineErr error
+	}{
+		{
+			nextLine: []assertion{
+				{prefix: "a", want: true},
+				{prefix: "aa", want: true},
+				{prefix: "aaa", want: true},
+				{prefix: "bbb", want: false},
+				{prefix: "ccc", want: false},
+			},
+			nextNextLine: []assertion{
+				{prefix: "aaa", want: false},
+				{prefix: "bbb", want: true},
+				{prefix: "ccc", want: false},
+			},
+		},
+		{
+			nextLine: []assertion{
+				{prefix: "aaa", want: false},
+				{prefix: "bbb", want: true},
+				{prefix: "ccc", want: false},
+			},
+			nextNextLine: []assertion{
+				{prefix: "aaa", want: false},
+				{prefix: "bbb", want: false},
+				{prefix: "ccc", want: true},
+			},
+		},
+		{
+			nextLine: []assertion{
+				{prefix: "aaa", want: false},
+				{prefix: "bbb", want: false},
+				{prefix: "ccc", want: true},
+				{prefix: "ddd", want: false},
+			},
+			nextNextLine: []assertion{
+				{prefix: "aaa", want: false},
+				{prefix: "bbb", want: false},
+				{prefix: "ccc", want: false},
+				{prefix: "ddd", want: false},
+			},
+		},
+		{
+			nextLine: []assertion{
+				{prefix: "aaa", want: false},
+				{prefix: "bbb", want: false},
+				{prefix: "ccc", want: false},
+				{prefix: "ddd", want: false},
+			},
+			nextNextLine: []assertion{
+				{prefix: "aaa", want: false},
+				{prefix: "bbb", want: false},
+				{prefix: "ccc", want: false},
+				{prefix: "ddd", want: false},
+			},
+			wantReadLineErr: io.EOF,
+		},
+	}
+
+	for _, tc := range testsPerReadLine {
+		for _, assert := range tc.nextLine {
+			got, err := in.nextLineStartsWith(assert.prefix)
+			if err != nil {
+				t.Fatalf("nextLineStartsWith returned unexpected error: %s", err)
+			}
+
+			if got != assert.want {
+				t.Fatalf("unexpected result for prefix %q. got=%t, want=%t", assert.prefix, got, assert.want)
+			}
+		}
+
+		for _, assert := range tc.nextNextLine {
+			got, err := in.nextNextLineStartsWith(assert.prefix)
+			if err != nil {
+				t.Fatalf("nextLineStartsWith returned unexpected error: %s", err)
+			}
+
+			if got != assert.want {
+				t.Fatalf("unexpected result for prefix %q. got=%t, want=%t", assert.prefix, got, assert.want)
+			}
+		}
+
+		_, err := in.readLine()
+		if err != tc.wantReadLineErr {
+			t.Fatalf("readLine returned unexpected error. got=%s, want=%s", err, tc.wantReadLineErr)
+		}
+
+	}
+}