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Add validation function for text fragment
Applying a fragment requires the content to match the stored counts, so there must be a way to check this. Parsed fragments should always be valid, but manually created or modified fragments may be invalid.
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‎gitdiff/gitdiff.go‎

Lines changed: 66 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -61,6 +61,72 @@ func (f *TextFragment) Header() string {
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return fmt.Sprintf("@@ -%d,%d +%d,%d @@ %s", f.OldPosition, f.OldLines, f.NewPosition, f.NewLines, f.Comment)
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}
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// Validate checks that the fragment is self-consistent and appliable. Validate
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// returns an error if and only if the fragment is invalid.
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func (f *TextFragment) Validate() error {
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var (
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oldLines, newLines int64
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leadingContext, trailingContext int64
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contextLines, addedLines, deletedLines int64
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)
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// count the types of lines in the fragment content
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for i, line := range f.Lines {
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switch line.Op {
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case OpContext:
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oldLines++
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newLines++
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contextLines++
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if addedLines == 0 && deletedLines == 0 {
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leadingContext++
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} else {
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trailingContext++
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}
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case OpAdd:
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newLines++
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addedLines++
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trailingContext = 0
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case OpDelete:
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oldLines++
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deletedLines++
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trailingContext = 0
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default:
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return fmt.Errorf("unknown operator %q on line %d", line.Op, i+1)
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}
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}
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// check the actual counts against the reported counts
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if oldLines != f.OldLines {
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return lineCountErr("old", oldLines, f.OldLines)
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}
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if newLines != f.NewLines {
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return lineCountErr("new", newLines, f.NewLines)
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}
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if leadingContext != f.LeadingContext {
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return lineCountErr("leading context", leadingContext, f.LeadingContext)
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}
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if trailingContext != f.TrailingContext {
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return lineCountErr("trailing context", trailingContext, f.TrailingContext)
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}
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if addedLines != f.LinesAdded {
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return lineCountErr("added", addedLines, f.LinesAdded)
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}
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if deletedLines != f.LinesDeleted {
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return lineCountErr("deleted", deletedLines, f.LinesDeleted)
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}
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// if a file is being created, it can only contain additions
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if f.OldPosition == 0 && f.OldLines != 0 {
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return fmt.Errorf("file creation fragment contains context or deletion lines")
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}
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return nil
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}
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func lineCountErr(kind string, actual, reported int64) error {
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return fmt.Errorf("fragment contains %d %s lines but reports %d", actual, kind, reported)
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}
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// Line is a line in a text fragment.
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type Line struct {
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Op LineOp

‎gitdiff/gitdiff_test.go‎

Lines changed: 161 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,161 @@
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package gitdiff
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import (
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"strings"
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"testing"
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)
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func TestTextFragmentValidate(t *testing.T) {
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tests := map[string]struct {
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Fragment TextFragment
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Err string
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}{
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"oldLines": {
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Fragment: TextFragment{
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OldPosition: 1,
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OldLines: 3,
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NewPosition: 1,
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NewLines: 2,
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LeadingContext: 1,
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TrailingContext: 0,
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LinesAdded: 1,
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LinesDeleted: 1,
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Lines: []Line{
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{Op: OpContext, Line: "line 1\n"},
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{Op: OpDelete, Line: "old line 2\n"},
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{Op: OpAdd, Line: "new line 2\n"},
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},
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},
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Err: "2 old lines",
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},
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"newLines": {
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Fragment: TextFragment{
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OldPosition: 1,
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OldLines: 2,
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NewPosition: 1,
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NewLines: 3,
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LeadingContext: 1,
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TrailingContext: 0,
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LinesAdded: 1,
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LinesDeleted: 1,
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Lines: []Line{
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{Op: OpContext, Line: "line 1\n"},
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{Op: OpDelete, Line: "old line 2\n"},
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{Op: OpAdd, Line: "new line 2\n"},
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},
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},
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Err: "2 new lines",
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},
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"leadingContext": {
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Fragment: TextFragment{
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OldPosition: 1,
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OldLines: 2,
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NewPosition: 1,
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NewLines: 2,
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LeadingContext: 0,
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TrailingContext: 0,
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LinesAdded: 1,
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LinesDeleted: 1,
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Lines: []Line{
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{Op: OpContext, Line: "line 1\n"},
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{Op: OpDelete, Line: "old line 2\n"},
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{Op: OpAdd, Line: "new line 2\n"},
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},
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},
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Err: "1 leading context lines",
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},
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"trailingContext": {
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Fragment: TextFragment{
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OldPosition: 1,
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OldLines: 4,
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NewPosition: 1,
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NewLines: 3,
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LeadingContext: 1,
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TrailingContext: 1,
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LinesAdded: 1,
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LinesDeleted: 2,
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Lines: []Line{
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{Op: OpContext, Line: "line 1\n"},
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{Op: OpDelete, Line: "old line 2\n"},
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{Op: OpAdd, Line: "new line 2\n"},
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{Op: OpContext, Line: "line 3\n"},
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{Op: OpDelete, Line: "old line 4\n"},
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},
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},
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Err: "0 trailing context lines",
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},
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"linesAdded": {
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Fragment: TextFragment{
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OldPosition: 1,
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OldLines: 4,
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NewPosition: 1,
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NewLines: 3,
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LeadingContext: 1,
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TrailingContext: 0,
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LinesAdded: 2,
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LinesDeleted: 2,
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Lines: []Line{
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{Op: OpContext, Line: "line 1\n"},
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{Op: OpDelete, Line: "old line 2\n"},
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{Op: OpAdd, Line: "new line 2\n"},
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{Op: OpContext, Line: "line 3\n"},
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{Op: OpDelete, Line: "old line 4\n"},
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},
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},
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Err: "1 added lines",
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},
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"linesDeleted": {
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Fragment: TextFragment{
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OldPosition: 1,
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OldLines: 4,
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NewPosition: 1,
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NewLines: 3,
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LeadingContext: 1,
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TrailingContext: 0,
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LinesAdded: 1,
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LinesDeleted: 1,
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Lines: []Line{
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{Op: OpContext, Line: "line 1\n"},
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{Op: OpDelete, Line: "old line 2\n"},
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{Op: OpAdd, Line: "new line 2\n"},
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{Op: OpContext, Line: "line 3\n"},
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{Op: OpDelete, Line: "old line 4\n"},
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},
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},
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Err: "2 deleted lines",
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},
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"fileCreation": {
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Fragment: TextFragment{
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OldPosition: 0,
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OldLines: 2,
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NewPosition: 1,
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NewLines: 1,
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LeadingContext: 0,
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TrailingContext: 0,
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LinesAdded: 1,
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LinesDeleted: 2,
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Lines: []Line{
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{Op: OpDelete, Line: "old line 1\n"},
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{Op: OpDelete, Line: "old line 2\n"},
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{Op: OpAdd, Line: "new line\n"},
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},
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},
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Err: "creation fragment",
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},
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}
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for name, test := range tests {
148+
t.Run(name, func(t *testing.T) {
149+
err := test.Fragment.Validate()
150+
if test.Err == "" && err != nil {
151+
t.Fatalf("unexpected validation error: %v", err)
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}
153+
if test.Err != "" && err == nil {
154+
t.Fatal("expected validation error, but got nil")
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}
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if !strings.Contains(err.Error(), test.Err) {
157+
t.Fatalf("incorrect validation error: %q is not in %q", test.Err, err.Error())
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}
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})
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}
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}

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