Add support for unordered arrays (#30)

* feat: Add support for unordered arrays

- Use the "<<UNORDERED>>" directive as the first string in the unordered
  array to ignore ordering when comparing arrays.
- Adds unit tests for this new logic.
- Adds a big real-world payload integration test that should cover most
  of the features of this package in combination

* fix: Remove snippet of unreachable code

* docs: Explain <<UNORDERED>> in README

* docs: Explain <<UNORDERED>> in GoDocs

* docs: Add <<UNORDERED>> runnable example

* chore: Address self-review comments (#30)

README.md

@@ -83,6 +83,19 @@ func TestWhatever(t *testing.T) {
 
 The above will fail your tests because the `time` key was not present in the actual JSON, and the `uuid` was `null`.
 
+### Ignore ordering in arrays
+
+If your JSON payload contains an array with elements whose ordering is not deterministic, then you can use the `"<<UNORDERED>>"` directive as the first element of the array in question:
+
+```go
+func TestUnorderedArray(t *testing.T) {
+    ja := jsonassert.New(t)
+    payload := `["bar", "foo", "baz"]`
+    ja.Assertf(payload, `["foo", "bar", "baz"]`)                  // Order matters, will fail your test.
+    ja.Assertf(payload, `["<<UNORDERED>>", "foo", "bar", "baz"]`) // Order agnostic, will pass your test.
+}
+```
+
 ## Docs
 
 You can find the [GoDocs for this package here](https://pkg.go.dev/github.com/kinbiko/jsonassert).

array.go

@@ -7,6 +7,71 @@ import (
 )
 
 func (a *Asserter) checkArray(path string, act, exp []interface{}) {
+	a.tt.Helper()
+	if len(exp) > 0 && exp[0] == "<<UNORDERED>>" {
+		a.checkArrayUnordered(path, act, exp[1:])
+	} else {
+		a.checkArrayOrdered(path, act, exp)
+	}
+}
+
+func (a *Asserter) checkArrayUnordered(path string, act, exp []interface{}) {
+	a.tt.Helper()
+	if len(act) != len(exp) {
+		a.tt.Errorf("length of arrays at '%s' were different. Expected array to be of length %d, but contained %d element(s)", path, len(exp), len(act))
+		serializedAct, serializedExp := serialize(act), serialize(exp)
+		if len(serializedAct+serializedExp) < 50 {
+			a.tt.Errorf("actual JSON at '%s' was: %+v, but expected JSON was: %+v, potentially in a different order", path, serializedAct, serializedExp)
+		} else {
+			a.tt.Errorf("actual JSON at '%s' was:\n%+v\nbut expected JSON was:\n%+v,\npotentially in a different order", path, serializedAct, serializedExp)
+		}
+		return
+	}
+
+	for i, actEl := range act {
+		found := false
+		for _, expEl := range exp {
+			if a.deepEqual(actEl, expEl) {
+				found = true
+			}
+		}
+		if !found {
+			serializedEl := serialize(actEl)
+			if len(serializedEl) < 50 {
+				a.tt.Errorf("actual JSON at '%s[%d]' contained an unexpected element: %s", path, i, serializedEl)
+			} else {
+				a.tt.Errorf("actual JSON at '%s[%d]' contained an unexpected element:\n%s", path, i, serializedEl)
+			}
+		}
+	}
+
+	for i, expEl := range exp {
+		found := false
+		for _, actEl := range act {
+			found = found || a.deepEqual(expEl, actEl)
+		}
+		if !found {
+			serializedEl := serialize(expEl)
+			if len(serializedEl) < 50 {
+				a.tt.Errorf("expected JSON at '%s[%d]': %s was missing from actual payload", path, i, serializedEl)
+			} else {
+				a.tt.Errorf("expected JSON at '%s[%d]':\n%s\nwas missing from actual payload", path, i, serializedEl)
+			}
+		}
+	}
+}
+
+func (a *Asserter) deepEqual(act, exp interface{}) bool {
+	// There's a non-zero chance that JSON serialization will *not* be
+	// deterministic in the future like it is in v1.16.
+	// However, until this is the case, I can't seem to find a test case that
+	// makes this evaluation return a false positive.
+	// The benefit is a lot of simplicity and considerable performance benefits
+	// for large nested structures.
+	return serialize(act) == serialize(exp)
+}
+
+func (a *Asserter) checkArrayOrdered(path string, act, exp []interface{}) {
 	a.tt.Helper()
 	if len(act) != len(exp) {
 		a.tt.Errorf("length of arrays at '%s' were different. Expected array to be of length %d, but contained %d element(s)", path, len(exp), len(act))
@@ -28,9 +93,6 @@ func extractArray(s string) ([]interface{}, error) {
 	if len(s) == 0 {
 		return nil, fmt.Errorf("cannot parse empty string as array")
 	}
-	if s[0] != '[' {
-		return nil, fmt.Errorf("cannot parse '%s' as array", s)
-	}
 	var arr []interface{}
 	err := json.Unmarshal([]byte(s), &arr)
 	return arr, err

examples_test.go

@@ -44,3 +44,14 @@ func ExampleAsserter_Assertf_presenceOnly() {
 	//unexpected object key(s) ["hi"] found at '$'
 	//expected object key(s) ["hello"] missing at '$'
 }
+
+func ExampleAsserter_Assertf_unorderedArray() {
+	ja := jsonassert.New(t)
+	ja.Assertf(
+		`["zero", "one", "two"]`,
+		`["<<UNORDERED>>", "one", "two", "three"]`,
+	)
+	//output:
+	//actual JSON at '$[0]' contained an unexpected element: "zero"
+	//expected JSON at '$[2]': "three" was missing from actual payload
+}

exports.go

@@ -20,14 +20,23 @@ along with the "world" format argument. For example:
 
 	ja.Assertf(`{"hello": "world"}`, `{"hello":"%s"}`, "world")
 
-Additionally, you may wish to make assertions against the *presence* of a
-value, but not against its value. For example:
+You may wish to make assertions against the *presence* of a value, but not
+against its value. For example:
 
 	ja.Assertf(`{"uuid": "94ae1a31-63b2-4a55-a478-47764b60c56b"}`, `{"uuid":"<<PRESENCE>>"}`)
 
 will verify that the UUID field is present, but does not check its actual value.
 You may use "<<PRESENCE>>" against any type of value. The only exception is null, which
 will result in an assertion failure.
+
+If you don't know / care about the order of the elements in an array in your
+payload, you can ignore the ordering:
+
+	payload := `["bar", "foo", "baz"]`
+	ja.Assertf(payload, `["<<UNORDERED>>", "foo", "bar", "baz"]`)
+
+The above will verify that "foo", "bar", and "baz" are exactly the elements in
+the payload, but will ignore the order in which they appear.
 */
 package jsonassert
 
@@ -97,14 +106,23 @@ format-directive.
 
 	ja.Assertf(`{"averageTestScore": "99%"}`, `{"averageTestScore":"%s"}`, "99%")
 
-Additionally, you may wish to make assertions against the *presence* of a
-value, but not against its value. For example:
+You may wish to make assertions against the *presence* of a value, but not
+against its value. For example:
 
 	ja.Assertf(`{"uuid": "94ae1a31-63b2-4a55-a478-47764b60c56b"}`, `{"uuid":"<<PRESENCE>>"}`)
 
 will verify that the UUID field is present, but does not check its actual value.
 You may use "<<PRESENCE>>" against any type of value. The only exception is null, which
 will result in an assertion failure.
+
+If you don't know / care about the order of the elements in an array in your
+payload, you can ignore the ordering:
+
+	payload := `["bar", "foo", "baz"]`
+	ja.Assertf(payload, `["<<UNORDERED>>", "foo", "bar", "baz"]`)
+
+The above will verify that "foo", "bar", and "baz" are exactly the elements in
+the payload, but will ignore the order in which they appear.
 */
 func (a *Asserter) Assertf(actualJSON, expectedJSON string, fmtArgs ...interface{}) {
 	a.tt.Helper()