assert.Equal: "No newline at end of file" can be misleading

[marco-m]

hello,
consider a test comparing two strings that _do not end with a newline:

func TestNoNewline(t *testing.T) {
	want := "banana"
	have := "mango"
	assert.Equal(t, want, have)
}

the output will be:

    foo_test.go:156: Expected values to be equal:
        -banana
        \ No newline at end of file
        +mango
        \ No newline at end of file

which is quite confusing: sure, there is no newline at the end of the "file", but it is on purpose :-)

I would expect simply:

    foo_test.go:156: Expected values to be equal:
        -banana
        +mango

If I change diff() as follows:

diff --git a/assert.go b/assert.go
index d2df971a5f..1692e38afd 100644
--- a/assert.go
+++ b/assert.go
@@ -194,8 +194,8 @@ func diff[T any](lhs, rhs T) string {
    var lhss, rhss string
    // Special case strings so we get nice diffs.
    if l, ok := any(lhs).(string); ok {
-       lhss = l
-       rhss = any(rhs).(string)
+       lhss = l + "\n"
+       rhss = any(rhs).(string) + "\n"
    } else {
        lhss = repr.String(lhs, repr.Indent("  ")) + "\n"
        rhss = repr.String(rhs, repr.Indent("  ")) + "\n"

I get the following 4 cases, which seem reasonable to me:

Case 1

func TestNoNewline(t *testing.T) {
	want := "banana"
	have := "mango"
	assert.Equal(t, want, have)
}

gives:

    marco_test.go:12: Expected values to be equal:
        -banana
        +mango
--- FAIL: TestNoNewline (0.00s)

Case 2

func TestWithNewline1(t *testing.T) {
	want := "banana\n"
	have := "mango"
	assert.Equal(t, want, have)
}

gives:

    marco_test.go:18: Expected values to be equal:
        -banana
        -
        +mango
--- FAIL: TestWithNewline1 (0.00s)

Case 3

func TestWithNewline2(t *testing.T) {
	want := "banana"
	have := "mango\n"
	assert.Equal(t, want, have)
}

gives

    marco_test.go:24: Expected values to be equal:
        -banana
        +mango
        +
--- FAIL: TestWithNewline2 (0.00s)

Case 4

func TestWithNewline(t *testing.T) {
	want := "banana\n"
	have := "mango\n"
	assert.Equal(t, want, have)
}

gives:

    marco_test.go:18: Expected values to be equal:
        -banana
        +mango
                                        <-- blank like, but doesn't seem to be a problem
--- FAIL: TestWithNewline (0.00s)

If you see value, I will be happy to provide a PR.