initial checkin

Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com>

monoid/testing/rules.go

@@ -0,0 +1,28 @@
+package testing
+
+import (
+	"testing"
+
+	AR "github.com/ibm/fp-go/internal/array"
+	M "github.com/ibm/fp-go/monoid"
+	"github.com/stretchr/testify/assert"
+)
+
+func assertLaws[A any](t *testing.T, m M.Monoid[A]) func(a A) bool {
+	e := m.Empty()
+	return func(a A) bool {
+		return assert.Equal(t, a, m.Concat(a, e), "Monoid right identity") &&
+			assert.Equal(t, a, m.Concat(e, a), "Monoid left identity")
+	}
+}
+
+// AssertLaws asserts the monoid laws for a dataset
+func AssertLaws[A any](t *testing.T, m M.Monoid[A]) func(data []A) bool {
+	law := assertLaws(t, m)
+
+	return func(data []A) bool {
+		return AR.Reduce(data, func(result bool, value A) bool {
+			return result && law(value)
+		}, true)
+	}
+}