test: Matching escaped and unescaped keys.

Note that this is affected by
humanwhocodes/momoa#164
in the sense that in JSON5 mode, unquoted escaped
keys are not yet unescaped in the same was as
all other keys, and will not trigger this lint
yet.  When the momoa issue is fixed, released, and
we have updated to that version, uncomment the
last test in no-duplicate-keys.test.js.

Suggest that we create a separate issue in this
repo to track that change.

Refs eslint#68

tests/rules/no-duplicate-keys.test.js

@@ -133,5 +133,61 @@ ruleTester.run("no-duplicate-keys", rule, {
 				},
 			],
 		},
+		{
+			code: '{"f\\u006fot": 1, "fo\\u006ft": 2}',
+			errors: [
+				{
+					messageId: "duplicateKey",
+					data: { key: "foot" },
+					line: 1,
+					column: 18,
+					endLine: 1,
+					endColumn: 29,
+				},
+			],
+		},
+		{
+			code: '{"f\\u006fot": 1, "fo\\u006ft": 2}',
+			language: "json/jsonc",
+			errors: [
+				{
+					messageId: "duplicateKey",
+					data: { key: "foot" },
+					line: 1,
+					column: 18,
+					endLine: 1,
+					endColumn: 29,
+				},
+			],
+		},
+		{
+			code: '{"f\\u006fot": 1, "fo\\u006ft": 2}',
+			language: "json/json5",
+			errors: [
+				{
+					messageId: "duplicateKey",
+					data: { key: "foot" },
+					line: 1,
+					column: 18,
+					endLine: 1,
+					endColumn: 29,
+				},
+			],
+		},
+		// See: https://github.com/humanwhocodes/momoa/issues/164
+		// {
+		// 	code: '{f\\u006fot: 1, fo\\u006ft: 2}',
+		// 	language: "json/json5",
+		// 	errors: [
+		// 		{
+		// 			messageId: "duplicateKey",
+		// 			data: { key: "foot" },
+		// 			line: 1,
+		// 			column: 18,
+		// 			endLine: 1,
+		// 			endColumn: 29,
+		// 		},
+		// 	],
+		// },
 	],
 });