SubJSONOf 

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

SubJSONOf operator allows to compare the JSON representation of data against expectedJSON. Unlike JSON operator, marshaled data must be a JSON object/map (aka {…}). expectedJSON can be a:

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

JSON data contained in expectedJSON must be a JSON object/map (aka {…}) too. During a match, each expected entry should match in the compared map. But some expected entries can be missing from the compared map.

type MyStruct struct {
  Name string `json:"name"`
  Age  int    `json:"age"`
}
got := MyStruct{
  Name: "Bob",
  Age:  42,
}
td.Cmp(t, got, td.SubJSONOf(`{"name": "Bob", "age": 42, "city": "NY"}`)) // succeeds
td.Cmp(t, got, td.SubJSONOf(`{"name": "Bob", "zip": 666}`))              // fails, extra "age"

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.SubJSONOf(`{"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.SubJSONOf(`{"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.

SubJSONOf 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.SubJSONOf(`{"foo":$1, "bar": 12}`, []int{1, 2, 3, 4}))
td.Cmp(t, gotValue,
  td.SubJSONOf(`{"foo":$1, "bar": 12}`, []any{1, 2, td.Between(2, 4), 4}))
td.Cmp(t, gotValue,
  td.SubJSONOf(`{"foo":$1, "bar": 12}`, 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, an encoding/json.RawMessage, a JSON filename or a io.Reader:

td.Cmp(t, gotValue, td.SubJSONOf("file.json", td.Between(12, 34)))
td.Cmp(t, gotValue, td.SubJSONOf([]byte(`[1, $1, 3]`), td.Between(12, 34)))
td.Cmp(t, gotValue, td.SubJSONOf(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.SubJSONOf(`{"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 SubJSONOf operator to simplify numeric tests.

Comments can be embedded in JSON data:

td.Cmp(t, gotValue,
  SubJSONOf(`
{
  // 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);
  • strings can contain non-escaped \n, \r and \t;
  • raw strings are accepted (r{raw}, r!raw!, …), see below;
  • int_lit & float_lit numbers as defined in go spec are accepted;
  • numbers can be prefixed by ‘+’.

Most operators can be directly embedded in SubJSONOf without requiring any placeholder. If an operators does not take any parameter, the parenthesis can be omitted.

td.Cmp(t, gotValue,
  td.SubJSONOf(`
{
  "fullname": HasPrefix("Foo"),
  "age":      Between(41, 43),
  "details":  SuperMapOf({
    "address": NotEmpty, // () are optional when no parameters
    "car":     Any("Peugeot", "Tesla", "Jeep") // any of these
  })
}`))

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

td.Cmp(t, gotValue,
  td.SubJSONOf(`{"fullname": HasPrefix($1), "bar": 42}`, "Zip"))

A few notes about operators embedding:

It is also possible to embed operators in JSON strings. This way, the JSON specification can be fulfilled. To avoid collision with possible strings, just prefix the first operator name with “$^”. The previous example becomes:

td.Cmp(t, gotValue,
  td.SubJSONOf(`
{
  "fullname": "$^HasPrefix(\"Foo\")",
  "age":      "$^Between(41, 43)",
  "details":  "$^SuperMapOf({
    \"address\": NotEmpty, // () are optional when no parameters
    \"car\":     Any(\"Peugeot\", \"Tesla\", \"Jeep\") // any of these
  })"
}`))

As you can see, in this case, strings in strings have to be escaped. Fortunately, newlines are accepted, but unfortunately they are forbidden by JSON specification. To avoid too much escaping, raw strings are accepted. A raw string is a “r” followed by a delimiter, the corresponding delimiter closes the string. The following raw strings are all the same as “foo\bar("zip")!”:

  • r’foo\bar"zip"!’
  • r,foo\bar"zip"!,
  • r%foo\bar"zip"!%
  • r(foo\bar(“zip”)!)
  • r{foo\bar(“zip”)!}
  • r[foo\bar(“zip”)!]
  • r<foo\bar(“zip”)!>

So non-bracketing delimiters use the same character before and after, but the 4 sorts of ASCII brackets (round, angle, square, curly) all nest: r[x[y]z] equals “x[y]z”. The end delimiter cannot be escaped.

With raw strings, the previous example becomes:

td.Cmp(t, gotValue,
  td.SubJSONOf(`
{
  "fullname": "$^HasPrefix(r<Foo>)",
  "age":      "$^Between(41, 43)",
  "details":  "$^SuperMapOf({
    r<address>: NotEmpty, // () are optional when no parameters
    r<car>:     Any(r<Peugeot>, r<Tesla>, r<Jeep>) // any of these
  })"
}`))

Note that raw strings are accepted anywhere, not only in original JSON strings.

To be complete, $^ can prefix an operator even outside a string. This is accepted for compatibility purpose as the first operator embedding feature used this way to embed some operators.

So the following calls are all equivalent:

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

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

Tip: when an io.Reader is expected to contain JSON data, it cannot be tested directly, but using the Smuggle operator simply solves the problem:

var body io.Reader
// …
td.Cmp(t, body, td.Smuggle(json.RawMessage{}, td.SubJSONOf(`{"foo":1,"bar":2}`)))
// or equally
td.Cmp(t, body, td.Smuggle(json.RawMessage(nil), td.SubJSONOf(`{"foo":1,"bar":2}`)))

Smuggle reads from body into an encoding/json.RawMessage then this buffer is unmarshaled by SubJSONOf operator before the comparison.

TypeBehind method returns the map[string]any type.

See also JSON, JSONPointer and SuperJSONOf.

See also SubJSONOf godoc.

Examples

Basic example
Placeholders example
File example

CmpSubJSONOf shortcut

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

CmpSubJSONOf is a shortcut for:

td.Cmp(t, got, td.SubJSONOf(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 CmpSubJSONOf godoc.

Examples

Basic example
Placeholders example
File example

T.SubJSONOf shortcut

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

SubJSONOf is a shortcut for:

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

See above for details.

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

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 T.SubJSONOf godoc.

Examples

Basic example
Placeholders example
File example