fix(corpus-sweep): name every missing binary, in flag order

Same map-ranging bug as the sibling tool, and this copy had no test on
the missing-binary path at all.

cmd/internal-tools/corpus-sweep/sweep_test.go

@@ -0,0 +1,46 @@
+package main
+
+import (
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+// Two binaries missing is one rerun, not two: the operator is told about both
+// at once, in flag order, whatever order the check happened to walk.
+func TestResolveBinaries_NamesEveryMissingBinaryInFlagOrder(t *testing.T) {
+	configuration := config{
+		campaignPath:   "campaign-that-is-not-installed",
+		sanderlingPath: "sanderling-that-is-not-installed",
+	}
+
+	err := resolveBinaries(&configuration)
+	if err == nil {
+		t.Fatal("got no error, want both missing binaries named")
+	}
+	message := err.Error()
+	campaign := strings.Index(message, "--campaign")
+	sanderling := strings.Index(message, "--sanderling")
+	if campaign < 0 || sanderling < 0 {
+		t.Fatalf("got %q, want both --campaign and --sanderling named", message)
+	}
+	if campaign > sanderling {
+		t.Errorf("got %q, want --campaign named before --sanderling", message)
+	}
+
+	resolved := config{
+		campaignPath: writeScript(
+			t,
+			filepath.Join(t.TempDir(), "stub-campaign"),
+			"#!/bin/sh\nexit 0\n",
+		),
+		sanderlingPath: "sanderling-that-is-not-installed",
+	}
+	err = resolveBinaries(&resolved)
+	if err == nil {
+		t.Fatal("got no error, want the missing sanderling named")
+	}
+	if strings.Contains(err.Error(), "--campaign") {
+		t.Errorf("got %q, want the campaign that resolved left out", err.Error())
+	}
+}