Added flatten operator

pkg/yqlib/operator_flatten_test.go

@@ -0,0 +1,48 @@
+package yqlib
+
+import (
+	"testing"
+)
+
+var flattenOperatorScenarios = []expressionScenario{
+	{
+		description:    "Flatten",
+		subdescription: "Recursively flattens all arrays",
+		document:       `[1, [2], [[3]]]`,
+		expression:     `flatten`,
+		expected: []string{
+			"D0, P[], (doc)::[1, 2, 3]\n",
+		},
+	},
+	{
+		description: "Flatten with depth of one",
+		document:    `[1, [2], [[3]]]`,
+		expression:  `flatten(1)`,
+		expected: []string{
+			"D0, P[], (doc)::[1, 2, [3]]\n",
+		},
+	},
+	{
+		description: "Flatten empty array",
+		document:    `[[]]`,
+		expression:  `flatten`,
+		expected: []string{
+			"D0, P[], (doc)::[]\n",
+		},
+	},
+	{
+		description: "Flatten array of objects",
+		document:    `[{foo: bar}, [{foo: baz}]]`,
+		expression:  `flatten`,
+		expected: []string{
+			"D0, P[], (doc)::[{foo: bar}, {foo: baz}]\n",
+		},
+	},
+}
+
+func TestFlattenOperatorScenarios(t *testing.T) {
+	for _, tt := range flattenOperatorScenarios {
+		testScenario(t, &tt)
+	}
+	documentScenarios(t, "Flatten", flattenOperatorScenarios)
+}