Auto fix missing newlines in Diff and DiffBytes (#80)

Author: FollowTheProcess

README.md

@@ -59,15 +59,15 @@ Will get you an error log in the test that looks like this...
 
 ```plaintext
 --- FAIL: TestDemo (0.00s)
-    test_test.go:501: 
+    test_test.go:501:
         Fruit scramble!
         ---------------
-        
+
         Got:    apples
         Wanted: oranges
-        
+
         (Apples are not oranges!)
-        
+
 FAIL
 ```
 
@@ -122,11 +122,11 @@ func TestTableThings(t *testing.T) {
             wantErr: true,
         },
     }
-    
+
     for _, tt := range tests {
         t.Run(tt.name, func(t *testing.T) {
             got, err := SomeFunction()
-    
+
             test.WantErr(t, err, tt.wantErr)
             test.Equal(t, got, tt.want)
         })
@@ -154,11 +154,11 @@ func TestTableThings(t *testing.T) {
             wantErr: true,
         },
     }
-    
+
     for _, tt := range tests {
         t.Run(tt.name, func(t *testing.T) {
             got, err := SomeFunction()
-    
+
             if tt.wantErr {
                 test.Err(t, err)
             } else {

test.go

@@ -367,20 +367,25 @@ func False(tb testing.TB, got bool, options ...Option) {
 
 // Diff fails if the two strings got and want are not equal and provides a rich
 // unified diff of the two for easy comparison.
+//
+// If either got or want do not end in a newline, one is added to avoid a
+// "No newline at end of file" warning in the diff which is visually distracting.
 func Diff(tb testing.TB, got, want string) {
 	tb.Helper()
-
-	// TODO(@FollowTheProcess): If either got or want don't end in a newline, add one
-	if diff := diff.Diff("want", []byte(want), "got", []byte(got)); diff != nil {
-		tb.Fatalf("\nDiff\n----\n%s\n", prettyDiff(string(diff)))
-	}
+	DiffBytes(tb, []byte(got), []byte(want))
 }
 
 // DiffBytes fails if the two []byte got and want are not equal and provides a rich
 // unified diff of the two for easy comparison.
+//
+// If either got or want do not end in a newline, one is added to avoid a
+// "No newline at end of file" warning in the diff which is visually distracting.
 func DiffBytes(tb testing.TB, got, want []byte) {
 	tb.Helper()
 
+	got = fixNL(got)
+	want = fixNL(want)
+
 	if diff := diff.Diff("want", want, "got", got); diff != nil {
 		tb.Fatalf("\nDiff\n----\n%s\n", prettyDiff(string(diff)))
 	}
@@ -508,3 +513,16 @@ func prettyDiff(diff string) string {
 
 	return strings.Join(lines, "\n")
 }
+
+// If data is empty or ends in \n, fixNL returns data.
+// Otherwise fixNL returns a new slice consisting of data with a final \n added.
+func fixNL(data []byte) []byte {
+	if len(data) == 0 || data[len(data)-1] == '\n' {
+		return data
+	}
+	d := make([]byte, len(data)+1)
+	copy(d, data)
+	d[len(data)] = '\n'
+
+	return d
+}

test_test.go

@@ -404,6 +404,16 @@ func TestTest(t *testing.T) {
 			},
 			wantFail: false,
 		},
+		{
+			name: "Diff/pass no trailing newline",
+			fn: func(tb testing.TB) {
+				got := "Some\nstuff here in this file\nlines as well wow\nsome more stuff"
+				want := "Some\nstuff here in this file\nlines as well wow\nsome more stuff"
+
+				test.Diff(tb, got, want)
+			},
+			wantFail: false,
+		},
 		{
 			name: "Diff/fail",
 			fn: func(tb testing.TB) {
@@ -413,6 +423,15 @@ func TestTest(t *testing.T) {
 			},
 			wantFail: true,
 		},
+		{
+			name: "Diff/fail no trailing newline",
+			fn: func(tb testing.TB) {
+				got := "Some\nstuff here in this file\nlines as well wow\nsome more stuff"
+				want := "Some\ndifferent stuff here in this file\nthis line is different\nsome more stuff"
+				test.Diff(tb, got, want)
+			},
+			wantFail: true,
+		},
 		{
 			name: "DiffBytes/pass",
 			fn: func(tb testing.TB) {

testdata/snapshots/TestTest/Diff/fail_no_trailing_newline.snap.txt

@@ -0,0 +1,14 @@
+
+Diff
+----
+diff want got
+--- want
++++ got
+@@ -1,4 +1,4 @@
+  Some
+- different stuff here in this file
+- this line is different
++ stuff here in this file
++ lines as well wow
+  some more stuff
+