Fix profile updates and validate configuration before apply

internal/budget/units_test.go

@@ -98,3 +98,38 @@ func TestNoSharedApps(t *testing.T) {
 		t.Fatal(got)
 	}
 }
+
+func TestSliceDropIns(t *testing.T) {
+	c := testConfig()
+	c.Units["compute"] = []string{"custom.slice"}
+	c.Prefixes["bulk"] = []string{"custom-.slice.d"}
+	files, err := c.render()
+	if err != nil {
+		t.Fatal(err)
+	}
+	for file, limit := range map[string]string{
+		"custom.slice.d/50-budget.conf": "16G", "custom-.slice.d/50-budget.conf": "8G",
+	} {
+		if text := files[file]; !strings.HasPrefix(text, "[Slice]\n") || !strings.Contains(text, "MemoryMax="+limit+"\n") {
+			t.Fatalf("%s: %q", file, text)
+		}
+	}
+	if got := c.unitProfile("custom-work.slice"); got != "bulk" {
+		t.Fatalf("slice prefix profile: %q", got)
+	}
+}
+
+func TestInvalidPrefixes(t *testing.T) {
+	for _, prefix := range []string{"snap-firefox", "snap.firefox", "snap.firefox.scope", "snap.firefox.timer.d"} {
+		t.Run(prefix, func(t *testing.T) {
+			c := testConfig()
+			c.Prefixes["default"] = []string{prefix}
+			if _, err := c.render(); err == nil {
+				t.Fatal("invalid prefix accepted")
+			}
+			if got := c.unitProfile("session-ui.service"); got != "" {
+				t.Fatalf("invalid prefix matched an unrelated unit: %q", got)
+			}
+		})
+	}
+}