Fix datetime comparisons

Broken since 2021 (06d0a36) 😅

Author: arp242

json.go

@@ -207,11 +207,11 @@ func (r Test) cmpAsDatetimes(kind, want, have string) Test {
 	if err != nil {
 		return r.bug("Could not read %q as a datetime value for key %q", want, r.Key)
 	}
-
-	haveT, err := time.Parse(layout, datetimeRepl.Replace(want))
+	haveT, err := time.Parse(layout, datetimeRepl.Replace(have))
 	if err != nil {
 		return r.failf("Malformed output from your encoder: key %q is not a datetime: %q", r.Key, have)
 	}
+
 	if !wantT.Equal(haveT) {
 		return r.failf("Values for key %q don't match:\n"+
 			"  Expected:     %v\n"+

json_test.go

@@ -5,14 +5,14 @@ import (
 )
 
 func TestCompareDatetime(t *testing.T) {
-	t.Skip() // TODO
-
 	tests := []struct {
 		kind, want, have string
 		wantFail         bool
 	}{
 		{"datetime", "2006-01-02T15:04:05.123Z", "2006-01-02T15:04:05.123Z", false},
 		{"datetime", "2006-01-02T15:04:05.123Z", "2006-01-02T15:04:05", true},
+		{"datetime", "2006-01-02T15:04:05+01:00", "2006-01-02T15:04:05+01:00", false},
+		{"datetime", "2006-01-02T15:04:05+01:00", "2006-01-02T15:04:05+01:01", true},
 		{"time-local", "15:04:05.123", "15:04:05.123", false},
 		{"time-local", "15:04:05.123", "15:04:05", true},
 	}