Allow FileTests to have trailing empty lines

This makes it easier to author template tests, because
editors tend to append a newline when saving files.

test/filetests/filetests.go

@@ -93,12 +93,12 @@ func (f FileTests) Run(t *testing.T) {
 				} else {
 					resultStr := testErr.UserErr().Error()
 					resultStr = regexp.MustCompile("__ytt_tpl\\d+_").ReplaceAllString(resultStr, "__ytt_tplXXX_")
-					resultStr = f.trimTrailingWhitespace(resultStr)
+					resultStr = TrimTrailingMultilineWhitespace(resultStr)
 
 					expectedStr = strings.TrimPrefix(expectedStr, "ERR:")
 					expectedStr = strings.TrimPrefix(expectedStr, " ")
 					expectedStr = strings.ReplaceAll(expectedStr, "__YTT_VERSION__", version.Version)
-					expectedStr = f.trimTrailingWhitespace(expectedStr)
+					expectedStr = TrimTrailingMultilineWhitespace(expectedStr)
 					err = f.expectEquals(resultStr, expectedStr)
 				}
 			case strings.HasPrefix(expectedStr, "OUTPUT POSITION:"):
@@ -134,14 +134,6 @@ func (f FileTests) Run(t *testing.T) {
 	}
 }
 
-func (f FileTests) trimTrailingWhitespace(multiLineString string) string {
-	var newLines []string
-	for _, line := range strings.Split(multiLineString, "\n") {
-		newLines = append(newLines, strings.TrimRight(line, "\t "))
-	}
-	return strings.Join(newLines, "\n")
-}
-
 func (f FileTests) asFilePositionsStr(result MarshalableResult) (string, error) {
 	printerFunc := func(w io.Writer) yamlmeta.DocumentPrinter {
 		return yamlmeta.WrappedFilePositionPrinter{yamlmeta.NewFilePositionPrinter(w)}
@@ -250,3 +242,15 @@ func (l DefaultTemplateLoader) Load(thread *starlark.Thread, module string) (sta
 		yttlibrary.NewDataModule(&l.DataValues, nil), nil, nil)
 	return api.FindModule(strings.TrimPrefix(module, "@ytt:"))
 }
+
+// TrimTrailingMultilineWhitespace returns a string with trailing whitespace trimmed from every line as well
+// as trimmed trailing empty lines
+func TrimTrailingMultilineWhitespace(s string) string {
+	var trimmedLines []string
+	for _, line := range strings.Split(s, "\n") {
+		trimmedLine := strings.TrimRight(line, "\t ")
+		trimmedLines = append(trimmedLines, trimmedLine)
+	}
+	multiline := strings.Join(trimmedLines, "\n")
+	return strings.TrimRight(multiline, "\n")
+}

test/filetests/filetests_test.go

@@ -0,0 +1,56 @@
+package filetests
+
+import (
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+func TestTrimTrailingMultilineWhitespace(t *testing.T) {
+	for _, testcase := range []struct {
+		give, want string
+	}{
+		{
+			give: `we want yaml`,
+			want: `we want yaml`,
+		},
+		{
+			give: `we want yaml `,
+			want: `we want yaml`,
+		},
+		{
+			give: `we want yaml	`,
+			want: `we want yaml`,
+		},
+		{
+			give: `we want yaml
+`,
+			want: `we want yaml`,
+		},
+		{
+			give: `
+we 
+want	
+yaml  `,
+			want: `
+we
+want
+yaml`,
+		},
+		{
+			give: `
+we
+
+  want	
+	yaml
+
+`,
+			want: `
+we
+
+  want
+	yaml`,
+		},
+	} {
+		assert.Equal(t, testcase.want, TrimTrailingMultilineWhitespace(testcase.give))
+	}
+}