diff --git a/internal/api/handlers/regions_test.go b/internal/api/handlers/regions_test.go
new file mode 100644
index 0000000..e5743ca
--- /dev/null
+++ b/internal/api/handlers/regions_test.go
@@ -0,0 +1,62 @@
+package handlers
+
+import (
+	"net/http"
+	"net/url"
+	"testing"
+)
+
+func TestParseIATAs_Single(t *testing.T) {
+	r := &http.Request{URL: &url.URL{RawQuery: "iata=yvr"}}
+	result := parseIATAs(r)
+	if len(result) != 1 || result[0] != "YVR" {
+		t.Errorf("expected [YVR], got %v", result)
+	}
+}
+
+func TestParseIATAs_Multiple(t *testing.T) {
+	r := &http.Request{URL: &url.URL{RawQuery: "iatas=yvr,yyj,yyc"}}
+	result := parseIATAs(r)
+	if len(result) != 3 {
+		t.Fatalf("expected 3 IATAs, got %d", len(result))
+	}
+	if result[0] != "YVR" || result[1] != "YYJ" || result[2] != "YYC" {
+		t.Errorf("unexpected IATAs: %v", result)
+	}
+}
+
+func TestParseIATAs_MultiplePreferredOverSingle(t *testing.T) {
+	// iatas param takes precedence over iata
+	r := &http.Request{URL: &url.URL{RawQuery: "iatas=yvr,yyj&iata=yyc"}}
+	result := parseIATAs(r)
+	if len(result) != 2 {
+		t.Fatalf("expected 2 IATAs, got %d", len(result))
+	}
+}
+
+func TestParseIATAs_Whitespace(t *testing.T) {
+	r := &http.Request{URL: &url.URL{RawQuery: "iatas=yvr%2C+yyj"}}
+	result := parseIATAs(r)
+	if len(result) != 2 {
+		t.Fatalf("expected 2 IATAs, got %d", len(result))
+	}
+	if result[1] != "YYJ" {
+		t.Errorf("expected YYJ after trimming whitespace, got %s", result[1])
+	}
+}
+
+func TestParseIATAs_Empty(t *testing.T) {
+	r := &http.Request{URL: &url.URL{RawQuery: ""}}
+	result := parseIATAs(r)
+	if result != nil {
+		t.Errorf("expected nil for empty query, got %v", result)
+	}
+}
+
+func TestParseIATAs_Uppercase(t *testing.T) {
+	r := &http.Request{URL: &url.URL{RawQuery: "iata=YVR"}}
+	result := parseIATAs(r)
+	if len(result) != 1 || result[0] != "YVR" {
+		t.Errorf("expected [YVR], got %v", result)
+	}
+}