add a few more tests, mini-refactor.

makefile

@@ -31,3 +31,6 @@ format: $(SRC)
 
 test: $(OUTPUT)
 	/bin/echo -e "123\n45 67" | ./$(OUTPUT)
+	/bin/echo -n "" | ./wc
+	./$(OUTPUT) $(SRC)
+	./$(OUTPUT) nonexistent_file || true

wc.c

@@ -2,11 +2,11 @@
 #include <unistd.h> // read, isatty
 
 // STDIN_FILENO
-int process_fp(int filenum)
+int process_fn(int fn)
 {
-    char buffer[1];
-    while (read(filenum, buffer, sizeof(buffer)) > 0) {
-        printf("%c", buffer[0]);
+    char c[1];
+    while (read(fn, c, sizeof(c)) > 0) {
+        printf("%c", c[0]);
     }
 		return 0;
 }
@@ -14,9 +14,17 @@ int process_fp(int filenum)
 int main(int argc, char** argv)
 {
     if (!isatty(STDIN_FILENO)) {
-        return process_fp(STDIN_FILENO);
+      return process_fn(STDIN_FILENO);
     } else if(argc > 1){
+			FILE* fp = fopen(argv[1], "r");
+			if(!fp){
+				perror("Could not open file");
+				return 1;
+			}
+			return process_fn(fileno(fp));
+		} else{
 			printf("To do");
+
 		}
     return 0;
 }