add tests

test/parser/samples/attribute-unique-binding-error/error.json

@@ -0,0 +1,10 @@
+{
+	"code": "duplicate-attribute",
+	"message": "Attributes need to be unique",
+	"start": {
+		"line": 1,
+		"column": 17,
+		"character": 17
+	},
+	"pos": 17
+}

test/parser/samples/attribute-unique-binding-error/input.svelte

@@ -0,0 +1 @@
+<Widget foo={42} bind:foo/>

test/parser/samples/attribute-unique-shorthand-error/error.json

@@ -0,0 +1,10 @@
+{
+	"code": "duplicate-attribute",
+	"message": "Attributes need to be unique",
+	"start": {
+		"line": 1,
+		"column": 17,
+		"character": 17
+	},
+	"pos": 17
+}

test/parser/samples/attribute-unique-shorthand-error/input.svelte

@@ -0,0 +1 @@
+<div title='foo' {title}></div>