Custom template for gotests to generate tests that perform stricter error testing

function.tmpl

{{define "function"}}
{{- $f := .}}

func {{.TestName}}(t *testing.T) {
	{{- with .Receiver}}
		{{- if .IsStruct}}
			{{- if .Fields}}
				type fields struct {
				{{- range .Fields}}
					{{Field .}} {{.Type}}
				{{- end}}
				}
			{{- end}}
		{{- end}}
	{{- end}}
	{{- if .TestParameters}}
	type args struct {
		{{- range .TestParameters}}
				{{Param .}} {{.Type}}
		{{- end}}
	}
	{{- end}}
	tests := []struct {
		name string
		{{- with .Receiver}}
			{{- if and .IsStruct .Fields}}
				fields fields
			{{- else}}
				{{Receiver .}} {{.Type}}
			{{- end}}
		{{- end}}
		{{- if .TestParameters}}
			args args
		{{- end}}
		{{- range .TestResults}}
			{{Want .}} {{.Type}}
		{{- end}}
		{{- if .ReturnsError}}
			wantErr error
		{{- end}}
	}{
		// TODO: Add test cases.
	}
	for {{if (or .Subtests (not .IsNaked))}} _, tt := {{end}} range tests {
        {{- if .Subtests }}t.Run(tt.name, func(t *testing.T) { {{- end -}}
			{{- with .Receiver}}
				{{- if .IsStruct}}
					{{Receiver .}} := {{if .Type.IsStar}}&{{end}}{{.Type.Value}}{
					{{- range .Fields}}
						{{.Name}}: tt.fields.{{Field .}},
					{{- end}}
					}
				{{- end}}
			{{- end}}
			{{- range .Parameters}}
				{{- if .IsWriter}}
					{{Param .}} := &bytes.Buffer{}
				{{- end}}
			{{- end}}
			{{- if and (not .OnlyReturnsError) (not .OnlyReturnsOneValue) }}
				{{template "results" $f}} {{template "call" $f}}
			{{- end}}
			{{- if .ReturnsError}}
				if {{if .OnlyReturnsError}} err := {{template "call" $f}}; {{end}} tt.wantErr != nil && !reflect.DeepEqual(err, tt.wantErr) {
					t.Errorf("{{template "message" $f}} error = %v, wantErr %v", {{template "inputs" $f}} err, tt.wantErr)
					{{- if .TestResults}}
						{{if .Subtests }}return{{else}}continue{{end}}
					{{- end}}
				}
			{{- end}}
			{{- range .TestResults}}
				{{- if .IsWriter}}
					if {{Got .}} := {{Param .}}.String(); {{Got .}} != tt.{{Want .}} {
				{{- else if .IsBasicType}}
					if {{if $f.OnlyReturnsOneValue}}{{Got .}} := {{template "inline" $f}}; {{end}} {{Got .}} != tt.{{Want .}} {
				{{- else}}
					if {{if $f.OnlyReturnsOneValue}}{{Got .}} := {{template "inline" $f}}; {{end}} !reflect.DeepEqual({{Got .}}, tt.{{Want .}}) {
				{{- end}}
				t.Errorf("{{template "message" $f}} {{if $f.ReturnsMultiple}}{{Got .}} {{end}}= %v, want %v", {{template "inputs" $f}} {{Got .}}, tt.{{Want .}})
				}
			{{- end}}
		{{- if .Subtests }} }) {{- end -}}
	}
}

{{end}}