tests: add testing around set and es aggregate

pkg/set/set_test.go

@@ -0,0 +1,25 @@
+package set_test
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/matryer/is"
+	"github.com/sour-is/ev/pkg/set"
+)
+
+func TestStringSet(t *testing.T) {
+	is := is.New(t)
+
+	s := set.New(strings.Fields("one two  three")...)
+
+	is.True(s.Has("one"))
+	is.True(s.Has("two"))
+	is.True(s.Has("three"))
+	is.True(!s.Has("four"))
+
+	is.Equal(set.New("one").String(), "set(one)")
+
+	var n set.Set[string]
+	is.Equal(n.String(), "set(<nil>)")
+}