Fix = should have been ==. Add some tests for vm type asserts.

src/core/string.c

@@ -503,7 +503,7 @@ JanetBuffer *janet_pretty(JanetBuffer *buffer, int depth, Janet x) {
 
 static const char *typestr(Janet x) {
     JanetType t = janet_type(x);
-    return (t = JANET_ABSTRACT)
+    return (t == JANET_ABSTRACT)
         ? janet_abstract_type(janet_unwrap_abstract(x))->name
         : janet_type_names[t];
 }

test/helper.janet

@@ -21,6 +21,11 @@
      (print e)))
  x)
 
+(defmacro assert-error
+  [msg & forms]
+  (def errsym (keyword (gensym)))
+  ~(assert (= ,errsym (try (do ,;forms) ([_] ,errsym))) ,msg))
+
 (defn start-suite [x]
  (set suite-num x)
  (print "\nRunning test suite " x " tests...\n  "))

test/suite3.janet

@@ -122,4 +122,11 @@
 (def spot (make-dog "spot"))
 (assert (= "spot says hi!" (:bark spot "hi")) "oo 2")
 
+# Negative tests
+
+(assert-error "+ check types" (+ 1 ()))
+(assert-error "- check types" (- 1 ()))
+(assert-error "* check types" (* 1 ()))
+(assert-error "/ check types" (/ 1 ()))
+
 (end-suite)