tests: add an operator overloading test

vlib/v/tests/operator_overloading_with_string_interpolation_test.v

@@ -0,0 +1,75 @@
+struct Vec {
+	x int
+	y int
+}
+
+pub fn (a Vec) str() string {
+	return '{$a.x, $a.y}'
+}
+
+fn (a Vec) + (b Vec) Vec {
+	return Vec {
+		a.x + b.x,
+		a.y + b.y
+	}
+}
+
+fn (a Vec) - (b Vec) Vec {
+	return Vec {
+		a.x - b.x,
+		a.y - b.y
+	}
+}
+
+fn (a Vec) * (b Vec) Vec {
+	return Vec {
+		a.x * b.x,
+		a.y * b.y
+	}
+}
+
+fn (a Vec) / (b Vec) Vec {
+	return Vec {
+		a.x / b.x,
+		a.y / b.y
+	}
+}
+
+fn (a Vec) % (b Vec) Vec {
+	return Vec {
+		a.x % b.x,
+		a.y % b.y
+	}
+}
+
+fn test_operator_overloading_with_string_interpolation() {
+	a := Vec{2, 3}
+	b := Vec{4, 5}
+	    
+    c := a + b
+    assert a.x + b.x == c.x
+    assert a.y + b.y == c.y
+    
+    d := a - b
+    assert a.x - b.x == d.x
+    assert a.y - b.y == d.y
+    
+    e := a * b
+    assert a.x * b.x == e.x
+    assert a.y * b.y == e.y
+    
+    f := a / b
+    assert a.x / b.x == f.x
+    assert a.y / b.y == f.y
+    
+    g := a % b
+    assert a.x % b.x == g.x
+    assert a.y % b.y == g.y
+    
+    assert c.str() == '{6, 8}'
+    assert d.str() == '{-2, -2}'
+    assert e.str() == '{8, 15}'
+    assert f.str() == '{0, 0}'
+    assert g.str() == '{2, 3}'
+ 
+}