Shell: Add some tests for subshells

Author: https://github.com/alimpfard
Commit: 2488815bdb
Pull-request: https://github.com/SerenityOS/serenity/pull/3372
Reviewed-by: https://github.com/tomuta

Shell/Tests/subshell.sh

@@ -0,0 +1,28 @@
+#/bin/sh
+
+setopt --verbose
+
+rm -rf shell-test
+mkdir shell-test
+cd shell-test
+
+    # Simple sequence (grouping)
+    { echo test > testfile }
+    test "$(cat testfile)" = "test" || echo cannot write to file in subshell && exit 1
+
+    # Simple sequence - many commands
+    { echo test1 > testfile; echo test2 > testfile }
+    test "$(cat testfile)" = "test2" || echo cannot write to file in subshell 2 && exit 1
+
+
+    # Does it exit with the last exit code?
+    { test -z "a" }
+    exitcode=$?
+    test "$exitcode" -eq 1 || echo exits with $exitcode when it should exit with 1 && exit 1
+
+    { test -z "a" || echo test }
+    exitcode=$?
+    test "$exitcode" -eq 0 || echo exits with $exitcode when it should exit with 0 && exit 1
+
+cd ..
+rm -rf shell-test