feat: Add dummy game utility and enhance testing capabilities

- also improve argument handling

tests/test_cli.sh

@@ -0,0 +1,83 @@
+#!/bin/bash
+
+# A test suite for testing CLI argument permutations of gsplash
+
+GSPLASH="./build/gsplash"
+GAME="/bin/true"
+IMAGE="nonexistent.png" 
+
+if [ ! -f "$GSPLASH" ]; then
+    echo "Please run 'make' first to build gsplash."
+    exit 1
+fi
+
+export SDL_VIDEODRIVER=dummy
+
+pass=0
+fail=0
+
+run_test() {
+    local expected_status=$1
+    shift
+    local expected_log="$1"
+    shift
+    local desc="$1"
+    shift
+    
+    printf "Test: %-45s " "$desc"
+    
+    # Run the command and capture output
+    local output
+    output=$($GSPLASH "$@" 2>&1)
+    local status=$?
+    
+    local passed=true
+    local error_msg=""
+
+    if [ $status -ne $expected_status ]; then
+        passed=false
+        error_msg="Expected status $expected_status, got $status"
+    elif [ -n "$expected_log" ]; then
+        if ! echo "$output" | grep -q "$expected_log"; then
+            passed=false
+            error_msg="Expected log missing: $expected_log"
+        fi
+    fi
+
+    if $passed; then
+        echo "PASS"
+        pass=$((pass+1))
+    else
+        echo "FAIL ($error_msg)"
+        fail=$((fail+1))
+    fi
+}
+
+echo "=== Running CLI Argument Tests ==="
+
+# Valid combinations (0=STRETCH, 1=CENTER, 2=CROP)
+run_test 0 "mode=1" "Basic invocation" $IMAGE $GAME
+run_test 0 "mode=0" "Long mode: stretch" --mode=stretch $IMAGE $GAME
+run_test 0 "mode=1" "Long mode: center" --mode=center $IMAGE $GAME
+run_test 0 "mode=2" "Long mode: crop" --mode=crop $IMAGE $GAME
+run_test 0 "mode=0" "Long mode: fallback to stretch" --mode=invalid $IMAGE $GAME
+run_test 0 "mode=0" "Short mode: stretch" -m stretch $IMAGE $GAME
+run_test 0 "mode=1" "Short mode: center" -m center $IMAGE $GAME
+run_test 0 "mode=2" "Short mode: crop" -m crop $IMAGE $GAME
+run_test 0 "mode=0" "Short mode: fallback to stretch" -m whatever $IMAGE $GAME
+run_test 0 "mode=1" "With game arguments" $IMAGE $GAME arg1 arg2
+run_test 0 "mode=2" "Mode and game arguments" -m crop $IMAGE $GAME arg1 arg2
+
+# Invalid combinations (Usage errors, so we just check for status 1, no specific log needed)
+run_test 1 "" "No arguments"
+run_test 1 "" "Only image" $IMAGE
+run_test 1 "" "Missing arg for short mode (-m only)" -m $IMAGE
+run_test 1 "" "Missing game for short mode" -m stretch $IMAGE
+
+echo "================================================="
+echo "Tests completed: $pass passed, $fail failed."
+
+if [ $fail -gt 0 ]; then
+    exit 1
+fi
+exit 0