Test the US places' reach by the locality table's population column, read by its header

data_test.go

@@ -4,6 +4,7 @@ import (
 	"io/fs"
 	"os"
 	"regexp"
+	"slices"
 	"strconv"
 	"strings"
 	"testing"
@@ -378,43 +379,42 @@ func TestShippedAddressIsOneNamedPick(t *testing.T) {
 // TestShippedPlacesSpreadAddresses pins that a city ships a tenth of its streets, not ten,
 // and that the US places reach below a town.
 func TestShippedPlacesSpreadAddresses(t *testing.T) {
-	cases := []struct {
-		country, city string
-		smallest      int
-	}{
-		{"SE", "Göteborg", 200},
-		{"US", "3651000", 2500},
-	}
-	for _, c := range cases {
+	for country, city := range map[string]string{"SE": "Göteborg", "US": "3651000"} {
 		streets := 0
-		for _, r := range geoRows(t, c.country, "street") {
-			if r[1] == c.city {
+		for _, r := range geoRows(t, country, "street") {
+			if r[1] == city {
 				streets++
 			}
 		}
 		if streets < 100 {
-			t.Errorf("geo.%s: %s ships %d streets, want a tenth of its streets, at least 100", c.country, c.city, streets)
-		}
-		population := map[string]int{"SE": 2, "US": 3}[c.country]
-		smallest := -1
-		for _, r := range geoRows(t, c.country, "locality") {
-			if n, err := strconv.Atoi(r[population]); err == nil && (smallest < 0 || n < smallest) {
-				smallest = n
-			}
-		}
-		if smallest < 0 || smallest > c.smallest {
-			t.Errorf("geo.%s: the smallest locality holds %d people, want one of %d or fewer", c.country, smallest, c.smallest)
+			t.Errorf("geo.%s: %s ships %d streets, want a tenth of its streets, at least 100", country, city, streets)
 		}
 	}
+	header, _, _ := strings.Cut(geoTSV(t, "US", "locality"), "\n")
+	population := slices.Index(strings.Split(header, "\t"), "population")
+	for _, r := range geoRows(t, "US", "locality") {
+		n, err := strconv.Atoi(r[population])
+		if err != nil {
+			t.Fatal(err)
+		}
+		if n < 2500 {
+			return
+		}
+	}
+	t.Error("geo.US: every locality holds 2500 people or more, want places drawn down to villages")
 }
 
-func geoRows(t *testing.T, country, table string) [][]string {
+func geoTSV(t *testing.T, country, table string) string {
 	b, err := os.ReadFile("data/geo/" + country + "/" + table + ".tsv")
 	if err != nil {
 		t.Fatal(err)
 	}
+	return strings.TrimSpace(string(b))
+}
+
+func geoRows(t *testing.T, country, table string) [][]string {
 	var out [][]string
-	for _, line := range strings.Split(strings.TrimSpace(string(b)), "\n")[1:] {
+	for _, line := range strings.Split(geoTSV(t, country, table), "\n")[1:] {
 		out = append(out, strings.Split(line, "\t"))
 	}
 	return out