Add simple full file parsing test

For now, this uses JSON to print objects on error, which is hard to
debug. It should probably use something like google/go-cmp instead,
because these objects are now too large for direct comparison.

Author: bluekeyes

gitdiff/parser_test.go

@@ -2,6 +2,7 @@ package gitdiff
 
 import (
 	"bufio"
+	"encoding/json"
 	"io"
 	"os"
 	"reflect"
@@ -223,6 +224,98 @@ a wild fragment appears?
 	}
 }
 
+func TestParse(t *testing.T) {
+	tests := map[string]struct {
+		InputFile string
+		Output    []*File
+		Err       bool
+	}{
+		"singleFile": {
+			InputFile: "testdata/single_file.patch",
+			Output: []*File{
+				{
+					OldName:      "dir/file.txt",
+					NewName:      "dir/file.txt",
+					OldMode:      os.FileMode(0100644),
+					OldOIDPrefix: "ebe9fa54",
+					NewOIDPrefix: "fe103e1d",
+					Fragments: []*Fragment{
+						{
+							OldPosition: 3,
+							OldLines:    6,
+							NewPosition: 3,
+							NewLines:    8,
+							Comment:     "fragment 1",
+							Lines: []FragmentLine{
+								{OpContext, "context line\n"},
+								{OpDelete, "old line 1\n"},
+								{OpDelete, "old line 2\n"},
+								{OpContext, "context line\n"},
+								{OpAdd, "new line 1\n"},
+								{OpAdd, "new line 2\n"},
+								{OpAdd, "new line 3\n"},
+								{OpContext, "context line\n"},
+								{OpDelete, "old line 3\n"},
+								{OpAdd, "new line 4\n"},
+								{OpAdd, "new line 5\n"},
+							},
+							LinesAdded:     5,
+							LinesDeleted:   3,
+							LeadingContext: 1,
+						},
+						{
+							OldPosition: 31,
+							OldLines:    2,
+							NewPosition: 33,
+							NewLines:    2,
+							Comment:     "fragment 2",
+							Lines: []FragmentLine{
+								{OpContext, "context line\n"},
+								{OpDelete, "old line 4\n"},
+								{OpAdd, "new line 6\n"},
+							},
+							LinesAdded:     1,
+							LinesDeleted:   1,
+							LeadingContext: 1,
+						},
+					},
+				},
+			},
+		},
+	}
+
+	for name, test := range tests {
+		t.Run(name, func(t *testing.T) {
+			f, err := os.Open(test.InputFile)
+			if err != nil {
+				t.Fatalf("unexpected error opening input file: %v", err)
+			}
+
+			files, err := Parse(f)
+			if test.Err {
+				if err == nil || err == io.EOF {
+					t.Fatalf("expected error parsing patch, but got %v", err)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("unexpected error parsing patch: %v", err)
+			}
+
+			if len(test.Output) != len(files) {
+				t.Fatalf("incorrect number of parsed files: expected %d, actual %d", len(test.Output), len(files))
+			}
+			for i := range test.Output {
+				if !reflect.DeepEqual(test.Output[i], files[i]) {
+					exp, _ := json.MarshalIndent(test.Output[i], "", "  ")
+					act, _ := json.MarshalIndent(files[i], "", "  ")
+					t.Errorf("incorrect file at position %d\nexpected: %s\nactual: %s", i, exp, act)
+				}
+			}
+		})
+	}
+}
+
 func newTestParser(input string, init bool) *parser {
 	p := &parser{r: bufio.NewReader(strings.NewReader(input))}
 	if init {

gitdiff/testdata/single_file.patch

@@ -0,0 +1,28 @@
+commit 5d9790fec7d95aa223f3d20936340bf55ff3dcbe
+Author: Morton Haypenny <mhaypenny@example.com>
+Date:   Tue Apr 2 22:55:40 2019 -0700
+
+    A single file with multiple fragments.
+
+    The content is arbitrary.
+
+diff --git a/dir/file.txt b/dir/file.txt
+index ebe9fa54..fe103e1d 100644
+--- a/dir/file.txt
++++ b/dir/file.txt
+@@ -3,6 +3,8 @@ fragment 1
+ context line
+-old line 1
+-old line 2
+ context line
++new line 1
++new line 2
++new line 3
+ context line
+-old line 3
++new line 4
++new line 5
+@@ -31,2 +33,2 @@ fragment 2
+ context line
+-old line 4
++new line 6