Merge mssql and dfsr expandEnabledCollectors func

Move to common collector.go and add function test.

Signed-off-by: Ben Reedy <breed808@breed808.com>

collector/collector_test.go

@@ -0,0 +1,34 @@
+package collector
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestExpandChildCollectors(t *testing.T) {
+	cases := []struct {
+		name           string
+		input          string
+		expectedOutput []string
+	}{
+		{
+			name:           "simple",
+			input:          "testing1,testing2,testing3",
+			expectedOutput: []string{"testing1", "testing2", "testing3"},
+		},
+		{
+			name:           "duplicate",
+			input:          "testing1,testing2,testing2,testing3",
+			expectedOutput: []string{"testing1", "testing2", "testing3"},
+		},
+	}
+
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			output := expandEnabledChildCollectors(c.input)
+			if !reflect.DeepEqual(output, c.expectedOutput) {
+				t.Errorf("Output mismatch, expected %+v, got %+v", c.expectedOutput, output)
+			}
+		})
+	}
+}