go-testdeep > Operators > JSON

JSON

func JSON(expectedJSON any, params ...any) TestDeep

JSON operator allows to compare the JSON representation of data against expectedJSON. expectedJSON can be a:

string containing JSON data like {"fullname":"Bob","age":42}
string containing a JSON filename, ending with “.json” (its content is ioutil.ReadFile before unmarshaling)
[]byte containing JSON data
io.Reader stream containing JSON data (is ioutil.ReadAll before unmarshaling)

expectedJSON JSON value can contain placeholders. The params are for any placeholder parameters in expectedJSON. params can contain TestDeep operators as well as raw values. A placeholder can be numeric like $2 or named like $name and always references an item in params.

Numeric placeholders reference the n’th “operators” item (starting at 1). Named placeholders are used with Tag operator as follows:

td.Cmp(t, gotValue,
  td.JSON(`{"fullname": $name, "age": $2, "gender": $3}`,
    td.Tag("name", td.HasPrefix("Foo")), // matches $1 and $name
    td.Between(41, 43),                  // matches only $2
    "male"))                             // matches only $3

Note that placeholders can be double-quoted as in:

td.Cmp(t, gotValue,
  td.JSON(`{"fullname": "$name", "age": "$2", "gender": "$3"}`,
    td.Tag("name", td.HasPrefix("Foo")), // matches $1 and $name
    td.Between(41, 43),                  // matches only $2
    "male"))                             // matches only $3

It makes no difference whatever the underlying type of the replaced item is (= double quoting a placeholder matching a number is not a problem). It is just a matter of taste, double-quoting placeholders can be preferred when the JSON data has to conform to the JSON specification, like when used in a “.json” file.

JSON does its best to convert back the JSON corresponding to a placeholder to the type of the placeholder or, if the placeholder is an operator, to the type behind the operator. Allowing to do things like:

td.Cmp(t, gotValue, td.JSON(`{"foo":$1}`, []int{1, 2, 3, 4}))
td.Cmp(t, gotValue,
  td.JSON(`{"foo":$1}`, []any{1, 2, td.Between(2, 4), 4}))
td.Cmp(t, gotValue, td.JSON(`{"foo":$1}`, td.Between(27, 32)))

Of course, it does this conversion only if the expected type can be guessed. In the case the conversion cannot occur, data is compared as is, in its freshly unmarshaled JSON form (so as bool, float64, string, []any, map[string]any or simply nil).

Note expectedJSON can be a []byte, a JSON filename or a io.Reader:

td.Cmp(t, gotValue, td.JSON("file.json", td.Between(12, 34)))
td.Cmp(t, gotValue, td.JSON([]byte(`[1, $1, 3]`), td.Between(12, 34)))
td.Cmp(t, gotValue, td.JSON(osFile, td.Between(12, 34)))

A JSON filename ends with “.json”.

To avoid a legit “$” string prefix causes a bad placeholder error, just double it to escape it. Note it is only needed when the “$” is the first character of a string:

td.Cmp(t, gotValue,
  td.JSON(`{"fullname": "$name", "details": "$$info", "age": $2}`,
    td.Tag("name", td.HasPrefix("Foo")), // matches $1 and $name
    td.Between(41, 43)))                 // matches only $2

For the “details” key, the raw value “$info” is expected, no placeholders are involved here.

Note that Lax mode is automatically enabled by JSON operator to simplify numeric tests.

Comments can be embedded in JSON data:

td.Cmp(t, gotValue,
  td.JSON(`
{
  // A guy properties:
  "fullname": "$name",  // The full name of the guy
  "details":  "$$info", // Literally "$info", thanks to "$" escape
  "age":      $2        /* The age of the guy:
                           - placeholder unquoted, but could be without
                             any change
                           - to demonstrate a multi-lines comment */
}`,
    td.Tag("name", td.HasPrefix("Foo")), // matches $1 and $name
    td.Between(41, 43)))                 // matches only $2

Comments, like in go, have 2 forms. To quote the Go language specification:

line comments start with the character sequence // and stop at the end of the line.
multi-lines comments start with the character sequence /* and stop with the first subsequent character sequence */.

Other JSON divergences:

‘,’ can precede a ‘}’ or a ‘]’ (as in go);
int_lit & float_lit numbers as defined in go spec are accepted;
numbers can be prefixed by ‘+’.

Most operators can be directly embedded in JSON without requiring any placeholder.

td.Cmp(t, gotValue,
  td.JSON(`
{
  "fullname": HasPrefix("Foo"),
  "age":      Between(41, 43),
  "details":  SuperMapOf({
    "address": NotEmpty(),
    "car":     Any("Peugeot", "Tesla", "Jeep") // any of these
  })
}`))

Placeholders can be used anywhere, even in operators parameters as in:

td.Cmp(t, gotValue, td.JSON(`{"fullname": HasPrefix($1)}`, "Zip"))

A few notes about operators embedding:

SubMapOf and SuperMapOf take only one parameter, a JSON object;
the optional 3rd parameter of Between has to be specified as a string and can be: “[]” or “BoundsInIn” (default), “[[” or “BoundsInOut”, “]]” or “BoundsOutIn”, “][” or “BoundsOutOut”;
not all operators are embeddable only the following are: All, Any, ArrayEach, Bag, Between, Contains, ContainsKey, Empty, Gt, Gte, HasPrefix, HasSuffix, Ignore, JSONPointer, Keys, Len, Lt, Lte, MapEach, N, NaN, Nil, None, Not, NotAny, NotEmpty, NotNaN, NotNil, NotZero, Re, ReAll, Set, SubBagOf, SubMapOf, SubSetOf, SuperBagOf, SuperMapOf, SuperSetOf, Values and Zero.

Operators taking no parameters can also be directly embedded in JSON data using $^OperatorName or “$^OperatorName” notation. They are named shortcut operators (they predate the above operators embedding but they still subsist for compatibility):

td.Cmp(t, gotValue, td.JSON(`{"id": $1}`, td.NotZero()))

can be written as:

td.Cmp(t, gotValue, td.JSON(`{"id": $^NotZero}`))

td.Cmp(t, gotValue, td.JSON(`{"id": "$^NotZero"}`))

As for placeholders, there is no differences between $^NotZero and “$^NotZero”.

The allowed shortcut operators follow:

Empty → $^Empty
Ignore → $^Ignore
NaN → $^NaN
Nil → $^Nil
NotEmpty → $^NotEmpty
NotNaN → $^NotNaN
NotNil → $^NotNil
NotZero → $^NotZero
Zero → $^Zero

TypeBehind method returns the reflect.Type of the expectedJSON once JSON unmarshaled. So it can be bool, string, float64, []any, map[string]any or any in case expectedJSON is “null”.

See also JSONPointer, SubJSONOf and SuperJSONOf.

See also JSON godoc.

Examples

Basic example

Placeholders example

Embedding example

File example

CmpJSON shortcut

func CmpJSON(t TestingT, got, expectedJSON any, params []any, args ...any) bool

CmpJSON is a shortcut for:

td.Cmp(t, got, td.JSON(expectedJSON, params...), args...)

See above for details.

Returns true if the test is OK, false if it fails.

If t is a *T then its Config field is inherited.

args… are optional and allow to name the test. This name is used in case of failure to qualify the test. If len(args) > 1 and the first item of args is a string and contains a ‘%’ rune then fmt.Fprintf is used to compose the name, else args are passed to fmt.Fprint. Do not forget it is the name of the test, not the reason of a potential failure.

See also CmpJSON godoc.

Examples

Basic example

Placeholders example

Embedding example

File example

T.JSON shortcut

func (t *T) JSON(got, expectedJSON any, params []any, args ...any) bool

JSON is a shortcut for:

t.Cmp(got, td.JSON(expectedJSON, params...), args...)

See above for details.

Returns true if the test is OK, false if it fails.

See also T.JSON godoc.

Examples

Basic example

Placeholders example

Embedding example

File example