You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: fstring_test.go
    path of file: ./repos/langchaingo/prompts/internal/fstring
    
    the code of the file until where you have to start completion: package fstring

import (
	"strings"
	"testing
    
func TestFormat(t *testing.T) {
	t.Parallel()

	type args struct {
		format string
		values map[string]any
	}
	tests := []struct {
		name    string
		args    args
		want    string
		wantErr string
	}{
		{"1", args{"{", map[string]any{}}, "", "single '{' is not allowed"},
		{"2", args{"{{", map[string]any{}}, "{", ""},
		{"3", args{"}", map[string]any{}}, "", "single '}' is not allowed"},
		{"4", args{"}}", map[string]any{}}, "}", ""},
		{"4", args{"{}", map[string]any{}}, "", "empty expression not allowed"},
		{"4", args{"{val}", map[string]any{}}, "", "args not defined"},
		{"4", args{"a={val}", map[string]any{"val": 1}}, "a=1", ""},
		{"4", args{"a= {val}", map[string]any{"val": 1}}, "a= 1", ""},
		{"4", args{"a= { val }", map[string]any{"val": 1}}, "a= 1", ""},
	}
	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()
			got, err := Format(tt.args.format, tt.args.values)
			if (err != nil) != (tt.wantErr != "") {
				t.Errorf("Format() error = %v, wantErr %v", err, tt.wantErr)
				return
			}
			if err != nil && !strings.Contains(err.Error(), tt.wantErr) {
				t.Errorf("Format() error = %v, wantErr %v", err, tt.wantErr)
				return
			}
			if got != tt.want {
				t.Errorf("Format() got = %v, want %v", got, tt.want)
			}
		})
	}
}