Added keys operator

pkg/yqlib/operator_keys_test.go

@@ -0,0 +1,47 @@
+package yqlib
+
+import (
+	"testing"
+)
+
+var keysOperatorScenarios = []expressionScenario{
+	{
+		description: "Map keys",
+		document:    `{dog: woof, cat: meow}`,
+		expression:  `keys`,
+		expected: []string{
+			"D0, P[], (!!seq)::- dog\n- cat\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `{}`,
+		expression: `keys`,
+		expected: []string{
+			"D0, P[], (!!seq)::[]\n",
+		},
+	},
+	{
+		description: "Array keys",
+		document:    `[apple, banana]`,
+		expression:  `keys`,
+		expected: []string{
+			"D0, P[], (!!seq)::- 0\n- 1\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `[]`,
+		expression: `keys`,
+		expected: []string{
+			"D0, P[], (!!seq)::[]\n",
+		},
+	},
+}
+
+func TestKeysOperatorScenarios(t *testing.T) {
+	for _, tt := range keysOperatorScenarios {
+		testScenario(t, &tt)
+	}
+	documentScenarios(t, "Keys", keysOperatorScenarios)
+}