fix

jsn.go

@@ -23,12 +23,14 @@ func (n N) MarshalJSON() ([]byte, error) {
 	return []byte(n), nil
 }
 
-// Unmarshal ...
+// Unmarshal only 1 JSON entity from the input.
+// Disallows unknown fields if the argument is a struct.
 func Unmarshal(b []byte, v any) error {
 	return UnmarshalFrom(bytes.NewReader(b), v)
 }
 
-// UnmarshalFrom ...
+// UnmarshalFrom only 1 JSON entity from the input.
+// Disallows unknown fields if the argument is a struct.
 func UnmarshalFrom(r io.Reader, v any) error {
 	d := json.NewDecoder(r)
 	d.DisallowUnknownFields()

jsn_test.go

@@ -0,0 +1,61 @@
+package jsn
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestUnmarshal(t *testing.T) {
+	testCases := []struct {
+		input  string
+		want   any
+		errStr string
+	}{
+		{
+			input: `"abc"`,
+			want:  "abc",
+		},
+		{
+			input: `123`,
+			want:  float64(123),
+		},
+		{
+			input: `{"abc": 123}`,
+			want:  map[string]any{"abc": float64(123)},
+		},
+		{
+			input: `{"abc": 123} `,
+			want:  map[string]any{"abc": float64(123)},
+		},
+		{
+			input: `        ["abc", 123] `,
+			want:  []any{"abc", float64(123)},
+		},
+		{
+			input:  `{"abc": 123}a`,
+			errStr: "body must contain only one JSON object",
+		},
+		{
+			input:  `{"abc`,
+			errStr: "unexpected EOF",
+		},
+	}
+
+	for _, tc := range testCases {
+		var val any
+		err := Unmarshal([]byte(tc.input), &val)
+		if err != nil {
+			if tc.errStr == "" {
+				t.Fatal(err)
+			}
+			if have := err.Error(); have != tc.errStr {
+				t.Fatalf("\nhave: %+v\nwant: %+v\n", have, tc.errStr)
+			}
+			continue
+		}
+
+		if !reflect.DeepEqual(val, tc.want) {
+			t.Fatalf("\nhave: %+v\nwant: %+v\n", val, tc.want)
+		}
+	}
+}