add test to validate platforms in gamedb

tests/04-gamedb-platforms.sh

@@ -0,0 +1,10 @@
+ACTUAL=$(cat gamedb.yaml | grep platform: | cut -d':' -f 2 | sort | uniq -c | tr -s ' ' | cut -d' ' -f 3 | tr '\n' ' ' | sed 's/ $//')
+EXPECTED="epic-store flathub gog steam"
+
+if [ "$ACTUAL" != "$EXPECTED" ]; then
+	echo "One or more invalid platforms detected."
+	echo
+	echo "Expected: '$EXPECTED'"
+	echo "Actual:   '$ACTUAL'"
+	exit 1
+fi

tests/run-all

@@ -5,3 +5,4 @@ set -e
 ./tests/01-gamedb-syntax.py
 ./tests/02-gamedb-duplicates.sh
 ./tests/03-hwdb-syntax.py
+./tests/04-gamedb-platforms.sh