Do not accept io.EOF when expecting an error

This should almost always be handled specially, so don't let tests that
expect errors hide the fact that they returned an io.EOF. This could be
revisited if the tests are ever updated to check for specific errors.

Author: bluekeyes

gitdiff/file_header_test.go

@@ -1,6 +1,7 @@
 package gitdiff
 
 import (
+	"io"
 	"os"
 	"reflect"
 	"testing"
@@ -152,8 +153,8 @@ index deadbeef
 
 			f, err := p.ParseGitFileHeader()
 			if test.Err {
-				if err == nil {
-					t.Fatalf("expected error parsing git file header, got nil")
+				if err == nil || err == io.EOF {
+					t.Fatalf("expected error parsing git file header, got %v", err)
 				}
 				return
 			}
@@ -257,8 +258,8 @@ context line
 
 			f, err := p.ParseTraditionalFileHeader()
 			if test.Err {
-				if err == nil {
-					t.Fatalf("expected error parsing traditional file header, got nil")
+				if err == nil || err == io.EOF {
+					t.Fatalf("expected error parsing traditional file header, got %v", err)
 				}
 				return
 			}
@@ -357,8 +358,8 @@ func TestParseName(t *testing.T) {
 		t.Run(name, func(t *testing.T) {
 			output, n, err := parseName(test.Input, test.Term, test.Drop)
 			if test.Err {
-				if err == nil {
-					t.Fatalf("expected error parsing name, but got nil")
+				if err == nil || err == io.EOF {
+					t.Fatalf("expected error parsing name, but got %v", err)
 				}
 				return
 			}
@@ -596,8 +597,8 @@ func TestParseGitHeaderData(t *testing.T) {
 
 			end, err := parseGitHeaderData(&f, test.Line, test.DefaultName)
 			if test.Err {
-				if err == nil {
-					t.Fatalf("expected error parsing header data, but got nil")
+				if err == nil || err == io.EOF {
+					t.Fatalf("expected error parsing header data, but got %v", err)
 				}
 				return
 			}