Change example code to follow "keep going" principle for testing

Author: just-an-engineer

_content/doc/tutorial/add-a-test.html

@@ -49,7 +49,7 @@
     want := regexp.MustCompile(`\b`+name+`\b`)
     msg, err := Hello("Gladys")
     if !want.MatchString(msg) || err != nil {
-        t.Fatalf(`Hello("Gladys") = %q, %v, want match for %#q, nil`, msg, err, want)
+        t.Errorf(`Hello("Gladys") = %q, %v, want match for %#q, nil`, msg, err, want)
     }
 }
 
@@ -58,7 +58,7 @@
 func TestHelloEmpty(t *testing.T) {
     msg, err := Hello("")
     if msg != "" || err == nil {
-        t.Fatalf(`Hello("") = %q, %v, want "", error`, msg, err)
+        t.Errorf(`Hello("") = %q, %v, want "", error`, msg, err)
     }
 }
 </pre