package mergo_test import ( "testing" "github.com/imdario/mergo" ) type Foo struct { Str string Bslice []byte } func TestIssue33Merge(t *testing.T) { dest := Foo{Str: "a"} toMerge := Foo{ Str: "b", Bslice: []byte{1, 2}, } if err := mergo.Merge(&dest, toMerge); err != nil { t.Errorf("Error while merging: %s", err) } // Merge doesn't overwrite an attribute if in destination it doesn't have a zero value. // In this case, Str isn't a zero value string. if dest.Str != "a" { t.Errorf("dest.Str should have not been override as it has a non-zero value: dest.Str(%v) != 'a'", dest.Str) } // If we want to override, we must use MergeWithOverwrite or Merge using WithOverride. if err := mergo.Merge(&dest, toMerge, mergo.WithOverride); err != nil { t.Errorf("Error while merging: %s", err) } if dest.Str != toMerge.Str { t.Errorf("dest.Str should have been override: dest.Str(%v) != toMerge.Str(%v)", dest.Str, toMerge.Str) } }