FIX: Substrings had corner-cases with incorrect results, read more

I found this while writing unit tests for Toy_Function, where one
(native) function was named 'identity' and another (custom) was named
'ident' to avoid a naming clash. The rename didn't resolve the clash, so
after some digging, I found that strings compared to substrings would
return a match, despite being different.

This took some awkward corner-case handling, as it turns out
'deepCompareUtil' only returns zero when no differences have been found,
not when a match has been found. I also added checks for this to
Toy_String's unit test, with the parameters checked in both orders i.e.
(a,b) and (b,a), because paranoia is your friend.

The rope pattern is powerful, but also gives you enough rope to hang
yourself.

tests/units/test_function.c

@@ -1,9 +1,145 @@
+#include "toy_vm.h"
 #include "toy_console_colors.h"
 
+#include "toy_lexer.h"
+#include "toy_parser.h"
+#include "toy_compiler.h"
+#include "toy_print.h"
+
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 
-int main(void) {
-	printf(TOY_CC_WARN "Test not yet implemented: %s\n" TOY_CC_RESET, __FILE__);
+//define a function in one bytecode, invoke it in another
+const char* sourceAlpha = "\n\
+//using the classic closure approach\n\
+fn makeCounter() {\n\
+	var counter: Int = 0;\n\
+\
+	fn increment() {\n\
+		return ++counter;\n\
+	}\n\
+\n\
+	return increment;\n\
+}\n\
+";
+
+const char* sourceBeta = "\n\
+var tally = makeCounter();\n\
+\n\
+while (true) {\n\
+	var result = tally();\n\
+\n\
+	print result;\n\
+\n\
+	if (result >= 10) {\n\
+		return result;\n\
+	}\n\
+}\n\
+";
+
+//utils
+unsigned char* makeCodeFromSource(Toy_Bucket** bucketHandle, const char* source) {
+	Toy_Lexer lexer;
+	Toy_bindLexer(&lexer, source);
+
+	Toy_Parser parser;
+	Toy_bindParser(&parser, &lexer);
+
+	Toy_Ast* ast = Toy_scanParser(bucketHandle, &parser);
+	return Toy_compileToBytecode(ast);
+}
+
+//tests
+int test_functions_from_bytecodes(void) {
+	//do the thing
+	{
+		//setup
+		Toy_Bucket* bucket = Toy_allocateBucket(TOY_BUCKET_IDEAL);
+		Toy_String* makeCounterString = Toy_createStringLength(&bucket, "makeCounter", 11);
+
+		Toy_VM vm;
+		Toy_initVM(&vm);
+
+		//run alpha
+		unsigned char* alpha = makeCodeFromSource(&bucket, sourceAlpha);
+		Toy_bindVM(&vm, alpha, NULL);
+		Toy_runVM(&vm);
+
+		//check for the function was declared
+		if (Toy_isDeclaredScope(vm.scope, makeCounterString) != true) {
+			fprintf(stderr, TOY_CC_ERROR "ERROR: Failed to create the function '%s' from source\n" TOY_CC_RESET, makeCounterString->leaf.data);
+			Toy_freeString(makeCounterString);
+			Toy_freeVM(&vm);
+			Toy_freeBucket(&bucket);
+			free(alpha);
+			return -1;
+		}
+
+		//get the function and clean up
+		Toy_Value fnValue = Toy_copyValue(&bucket, *Toy_accessScopeAsPointer(vm.scope, makeCounterString));
+		Toy_resetVM(&vm, false, true);
+
+		//run beta
+		unsigned char* beta = makeCodeFromSource(&bucket, sourceBeta);
+		Toy_bindVM(&vm, beta, NULL);
+		Toy_declareScope(vm.scope, makeCounterString, TOY_VALUE_ANY, fnValue, true);
+		Toy_runVM(&vm);
+
+		//examine the results
+		if (vm.stack->count != 1 ||
+			TOY_VALUE_IS_INTEGER(vm.stack->data[0]) != true ||
+			TOY_VALUE_AS_INTEGER(vm.stack->data[0]) != 10
+		)
+		{
+			fprintf(stderr, TOY_CC_ERROR "ERROR: Unexpected result found in function results\n" TOY_CC_RESET);
+			Toy_freeString(makeCounterString);
+			Toy_freeVM(&vm);
+			Toy_freeBucket(&bucket);
+			free(alpha);
+			free(beta);
+			return -1;
+		}
+
+		Toy_resetVM(&vm, false, true);
+
+		//cleanup
+		Toy_freeValue(fnValue);
+		Toy_freeString(makeCounterString);
+		Toy_freeVM(&vm);
+		Toy_freeBucket(&bucket);
+		free(alpha);
+		free(beta);
+	}
+
+	//all good
 	return 0;
-}
+}
+
+int test_functions_from_callbacks(void) {
+	printf(TOY_CC_WARN "WIP test not yet implemented: %s\n" TOY_CC_RESET, __FILE__);
+	return 0;
+}
+
+int main(void) {
+	//run each test set, returning the total errors given
+	int total = 0, res = 0;
+
+	{
+		res = test_functions_from_bytecodes();
+		if (res == 0) {
+			printf(TOY_CC_NOTICE "All good\n" TOY_CC_RESET);
+		}
+		total += res;
+	}
+
+	{
+		res = test_functions_from_callbacks();
+		if (res == 0) {
+			printf(TOY_CC_NOTICE "All good\n" TOY_CC_RESET);
+		}
+		total += res;
+	}
+
+	return total;
+}