Added some additional tests and typechecking.

lib/template.js

@@ -7,11 +7,17 @@ module.exports = function(template) {
       if(!template.hasOwnProperty(expr))
         throw new Error("\"" + expr + "\" not found in language template.");
 
+      else if(typeof template[expr] !== "string" ||
+              /\$\d+/.test(template[expr]))
+        throw new Error("\"" + expr + "\" was used in a value context, but is expected in a template context.");
+
       else
         return template[expr];
     }
 
-    else if(Array.isArray(expr)) {
+    else if(Array.isArray(expr) &&
+            expr.length &&
+            typeof expr[0] === "string") {
       if(!template.hasOwnProperty(expr[0]))
         throw new Error("\"" + expr[0] + "\" not found in language template.");
 

test.js

@@ -1,31 +1,92 @@
 var expect      = require("chai").expect,
     fs          = require("fs"),
     path        = require("path"),
+    template    = require("./lib/template"),
     translation = require("./"),
     util        = require("util");
 
 describe("translation", function() {
-  fs.readdirSync(path.join(__dirname, "test-cases")).forEach(function(lang) {
-    if(lang.charAt(0) === ".")
-      return;
+  describe("template", function() {
+    var convert = template({
+          "foo": "bar",
+          "bar": "meeple $2",
+          "baz": function(a, b) { return "meeple " + b; }
+        });
 
-    var name      = path.basename(lang, ".json"),
-        translate = translation[name];
+    it("should return a number in string form", function() {
+      expect(convert(42)).to.equal("42");
+    });
+
+    it("should throw an error given an unrecognized string", function() {
+      expect(function() { convert("42"); }).to.throw();
+    });
+
+    it("should apply an expected value conversion", function() {
+      expect(convert("foo")).to.equal("bar");
+    });
+
+    it("should throw an error given a value that's expected to be a string template", function() {
+      expect(function() { convert("bar"); }).to.throw();
+    });
+
+    it("should throw an error given a value that's expected to be a function template", function() {
+      expect(function() { convert("baz"); }).to.throw();
+    });
+
+    it("should throw an error given an empty array", function() {
+      expect(function() { convert([]); }).to.throw();
+    });
+
+    it("should apply a string template", function() {
+      expect(convert(["bar", 10, 20])).to.equal("meeple 20");
+    });
+
+    it("should apply a function template", function() {
+      expect(convert(["baz", 10, 20])).to.equal("meeple 20");
+    });
+
+    it("should recursively apply function templates", function() {
+      /* Actually, a "meeple meeple bar" sounds like it'd be a pretty tasty
+       * candy treat. */
+      expect(convert(["bar", 10, ["baz", 20, "foo"]])).to.equal("meeple meeple bar");
+    });
+
+    it("should throw an error given undefined", function() {
+      expect(function() { convert(undefined); }).to.throw();
+    });
+
+    it("should throw an error given null", function() {
+      expect(function() { convert(null); }).to.throw();
+    });
+
+    it("should throw an error given an object", function() {
+      expect(function() { convert({}); }).to.throw();
+    });
+  });
+
+  describe("language", function() {
+    fs.readdirSync(path.join(__dirname, "test-cases")).forEach(function(lang) {
+      if(lang.charAt(0) === ".")
+        return;
+
+      var name      = path.basename(lang, ".json"),
+          translate = translation[name];
+
+      describe(name, function() {
+        var cases = JSON.parse(
+              fs.readFileSync(path.join(__dirname, "test-cases", lang))
+            );
+
+        Object.keys(cases).forEach(function(summary) {
+          var source = cases[summary];
 
-    describe(name, function() {
-      var cases = JSON.parse(
-            fs.readFileSync(path.join(__dirname, "test-cases", lang))
+          it(
+            util.format("should translate %j to \"%s\"", source, summary),
+            function() {
+              expect(translate(source)).to.equal(summary);
+            }
           );
-
-      Object.keys(cases).forEach(function(summary) {
-        var source = cases[summary];
-
-        it(
-          util.format("should translate %j to \"%s\"", source, summary),
-          function() {
-            expect(translate(source)).to.equal(summary);
-          }
-        );
+        });
       });
     });
   });