add test for keyword-alias declared as prefix

Author: pchampin

tests/expand-manifest.jsonld

@@ -2368,6 +2368,14 @@
       "option": {"specVersion": "json-ld-1.1"},
       "input": "expand/pr29-in.jsonld",
       "expect": "expand/pr29-out.jsonld"
+    }, {
+      "@id": "#tpr30",
+      "@type": ["jld:NegativeEvaluationTest", "jld:ExpandTest"],
+      "name": "Fails if trying to declare a keyword alias as prefix.",
+      "purpose": "Keyword aliases can not be used as prefixes.",
+      "option": {"specVersion": "json-ld-1.1"},
+      "input": "expand/pr30-in.jsonld",
+      "expect": "invalid term definition"
     }, {
       "@id": "#tso01",
       "@type": ["jld:NegativeEvaluationTest", "jld:ExpandTest"],

tests/expand/pr30-in.jsonld

@@ -0,0 +1,10 @@
+{
+  "@context": {
+    "@version": 1.1,
+    "foo": {
+      "@id": "@type",
+      "@prefix": true
+    }
+  },
+  "foo:bar": "http://example.org/baz"
+}