Handle invalid cases

Where-is-the-Arrow-Pointing/moul/witap.go

@@ -25,11 +25,20 @@ func NewResolverFromString(theMap string) Resolver {
 }
 
 func (r *Resolver) GetStartPosition() (Position, error) {
+	var found *Position
 	for y, line := range r.Lines {
-		if pos := strings.Index(line, "S"); pos != -1 {
-			return Position{pos, y}, nil
+		for x, char := range line {
+			if fmt.Sprintf("%c", char) == "S" {
+				if found != nil {
+					return Position{-1, -1}, fmt.Errorf("Multiple starting points")
+				}
+				found = &Position{x, y}
+			}
 		}
 	}
+	if found != nil {
+		return *found, nil
+	}
 	return Position{-1, -1}, fmt.Errorf("No such starting point")
 }
 
@@ -39,9 +48,9 @@ func (r *Resolver) Run() (string, error) {
 		return "", err
 	}
 
-	fmt.Println("===============================")
-	r.PrintMap()
-	fmt.Println("")
+	// fmt.Println("===============================")
+	// r.PrintMap()
+	// fmt.Println("")
 
 	return r.Step(startPos, Position{-1, -1})
 }

Where-is-the-Arrow-Pointing/moul/witap_test.go

@@ -70,10 +70,30 @@ O<|  |  |>O
   +-+++-+
 O<|  |  |>O
   +->E<-+
+`,
+	`
+6-----+
+|     +-^
++---+->B
+    +---^
+`,
+	`
+abc
+de
+`,
+	`
+S-S-S-+
+|     +-^
++---+->B
+    +---^
 `,
 }
 var outputs = []string{
-	"a", "b", "b", "Q", "A", "B", "Y", "B", "E",
+	"a", "b", "b", "Q", "A", "B", "Y", "B", "E", "", "", "",
+}
+
+var errs = []error{
+	nil, nil, nil, nil, nil, nil, nil, nil, nil, fmt.Errorf("No such starting point"), fmt.Errorf("No such starting point"), fmt.Errorf("Multiple starting points"),
 }
 
 func ExampleResolver_a() {
@@ -88,7 +108,7 @@ func TestResolver(t *testing.T) {
 			Convey(fmt.Sprintf("input %d", idx+1), func() {
 				resolver := NewResolverFromString(input[1 : len(input)-1])
 				output, err := resolver.Run()
-				So(err, ShouldBeNil)
+				So(err, ShouldResemble, errs[idx])
 				So(output, ShouldEqual, outputs[idx])
 			})
 		}