diff --git a/src/cbaselib.c b/src/cbaselib.c
index b6734bf..b763892 100644
--- a/src/cbaselib.c
+++ b/src/cbaselib.c
@@ -5,9 +5,15 @@
 #include "cmem.h"
 
 void cosmoB_loadLibrary(CState *state) {
+    // print
     cosmoV_pushString(state, "print");
     cosmoV_pushCFunction(state, cosmoB_print);
-    cosmoV_register(state, 1); // sets "print" global to cosmoB_print
+
+    // assert (for unit testing)
+    cosmoV_pushString(state, "assert");
+    cosmoV_pushCFunction(state, cosmoB_assert);
+
+    cosmoV_register(state, 2);
 }
 
 int cosmoB_print(CState *state, int nargs, CValue *args) {
@@ -20,6 +26,24 @@ int cosmoB_print(CState *state, int nargs, CValue *args) {
     return 0; // print doesn't return any args
 }
 
+int cosmoB_assert(CState *state, int nargs, CValue *args) {
+    if (nargs != 1) {
+        cosmoV_error(state, "assert() expected 1 argument, got %d!", nargs);
+        return 0; // nothing pushed onto the stack to return
+    }
+
+    if (!IS_BOOLEAN(args[0])) {
+        cosmoV_error(state, "assert() expected <boolean>, got %s!", cosmoV_typeStr(args[0]));
+        return 0;
+    }
+
+    if (!cosmoV_readBoolean(args[0])) { // expression passed was false, error!
+        cosmoV_error(state, "assert() failed!");
+    } // else do nothing :)
+
+    return 0;
+}
+
 int cosmoB_dsetProto(CState *state, int nargs, CValue *args) {
     if (nargs == 2) {
         CObjObject *obj = cosmoV_readObject(args[0]); // object to set proto too
@@ -35,7 +59,7 @@ int cosmoB_dsetProto(CState *state, int nargs, CValue *args) {
 
 int cosmoB_dgetProto(CState *state, int nargs, CValue *args) {
     if (nargs != 1) {
-        cosmoV_error(state, "Expected 1 parameter, got %d!", nargs);
+        cosmoV_error(state, "Expected 1 argument, got %d!", nargs);
     }
 
     cosmoV_pushValue(state, cosmoV_newObj(cosmoV_readObject(args[0])->proto)); // just return the proto
diff --git a/src/cbaselib.h b/src/cbaselib.h
index 9d9ef26..2b92971 100644
--- a/src/cbaselib.h
+++ b/src/cbaselib.h
@@ -7,6 +7,6 @@
 COSMO_API void cosmoB_loadLibrary(CState *state);
 COSMO_API void cosmoB_loadDebug(CState *state);
 COSMO_API int cosmoB_print(CState *state, int nargs, CValue *args);
-COSMO_API int cosmoB_foreach(CState *state, int nargs, CValue *args);
+COSMO_API int cosmoB_assert(CState *state, int nargs, CValue *args);
 
 #endif
\ No newline at end of file
diff --git a/src/cobj.h b/src/cobj.h
index 9e9a38a..e93e47e 100644
--- a/src/cobj.h
+++ b/src/cobj.h
@@ -64,7 +64,7 @@ typedef struct CObjFunction {
     CChunk chunk;
     int args;
     int upvals;
-    int variadic;
+    bool variadic;
     CObjString *name;
     CObjString *module; // name of the "module"
 } CObjFunction;
diff --git a/src/cosmo.h b/src/cosmo.h
index 7ee9b36..67b9185 100644
--- a/src/cosmo.h
+++ b/src/cosmo.h
@@ -7,8 +7,12 @@
 #include <stdbool.h>
 #include <stdio.h>
 
+#include <assert.h>
+
 //#define NAN_BOXXED
 
+#define COSMOASSERT(x) assert(x)
+
 // forward declare *most* stuff so our headers are cleaner
 typedef struct CState CState;
 typedef struct CChunk CChunk;
diff --git a/src/cvm.c b/src/cvm.c
index ba70e29..97c818c 100644
--- a/src/cvm.c
+++ b/src/cvm.c
@@ -173,7 +173,7 @@ bool call(CState *state, CObjClosure *closure, int args, int nresults, int offse
         state->top -= extraArgs;
 
         pushCallFrame(state, closure, func->args + 1);
-    } else if (args < func->args) { // too few args passed, obvious user error
+    } else if (args != func->args) { // mismatched args
         cosmoV_error(state, "Expected %d arguments for %s, got %d!", closure->function->args, closure->function->name == NULL ? UNNAMEDCHUNK : closure->function->name->str, args);
         return false;
     } else {