Invalid input error message (#540)

* Added check for type of expressions passed to parseTree function
* Added tests for bad input raising exception
* Added test for supported types NOT throwing exception
* Added test case for parser taking String objects

test/katex-spec.js

@@ -1382,6 +1382,33 @@ describe("An HTML font tree-builder", function() {
         span = "<span class=\"mord mathbb\" style=\"color:blue;\">R</span>";
         expect(markup).toContain(span);
     });
+
+    it("should throw TypeError when the expression is of the wrong type", function() {
+        expect(function() {
+            katex.renderToString({badInputType: "yes"});
+        }).toThrowError(TypeError);
+        expect(function() {
+            katex.renderToString([1, 2]);
+        }).toThrowError(TypeError);
+        expect(function() {
+            katex.renderToString(undefined);
+        }).toThrowError(TypeError);
+        expect(function() {
+            katex.renderToString(null);
+        }).toThrowError(TypeError);
+        expect(function() {
+            katex.renderToString(1.234);
+        }).toThrowError(TypeError);
+    });
+
+    it("should not throw TypeError when the expression is a supported type", function() {
+        expect(function() {
+            katex.renderToString("\\sqrt{123}");
+        }).not.toThrowError(TypeError);
+        expect(function() {
+            katex.renderToString(new String("\\sqrt{123}"));
+        }).not.toThrowError(TypeError);
+    });
 });
 
 
@@ -1878,3 +1905,15 @@ describe("A macro expander", function() {
         });
     });
 });
+
+describe("A parser taking String objects", function() {
+    it("should not fail on an empty String object", function() {
+        expect(new String("")).toParse();
+    });
+
+    it("should parse the same as a regular string", function() {
+        expect(new String("xy")).toParseLike("xy");
+        expect(new String("\\div")).toParseLike("\\div");
+        expect(new String("\\frac 1 2")).toParseLike("\\frac 1 2");
+    });
+});