diff --git a/src/uu/test/src/parser.rs b/src/uu/test/src/parser.rs
index dab0f8af6f9..85b9c5c5f0c 100644
--- a/src/uu/test/src/parser.rs
+++ b/src/uu/test/src/parser.rs
@@ -195,10 +195,11 @@ impl Parser {
     ///
     ///   EXPR → TERM | EXPR BOOLOP EXPR
     fn expr(&mut self) -> ParseResult<()> {
-        if !self.peek_is_boolop() {
+        let has_term = !self.peek_is_boolop();
+        if has_term {
             self.term()?;
         }
-        self.maybe_boolop()?;
+        self.maybe_boolop(has_term)?;
         Ok(())
     }
 
@@ -344,7 +345,7 @@ impl Parser {
                     _ => {
                         // bang is literal; parsing continues with op
                         self.literal(Symbol::Bang.into_literal())?;
-                        self.maybe_boolop()?;
+                        self.maybe_boolop(true)?;
                     }
                 }
             }
@@ -379,16 +380,28 @@ impl Parser {
 
     /// Peek at the next token and parse it as a BOOLOP or string literal,
     /// as appropriate.
-    fn maybe_boolop(&mut self) -> ParseResult<()> {
+    ///
+    /// `has_left_operand` tells whether an expression was already parsed for
+    /// the BOOLOP to apply to, which decides what a BOOLOP at the end of the
+    /// stream means.
+    fn maybe_boolop(&mut self, has_left_operand: bool) -> ParseResult<()> {
         if self.peek_is_boolop() {
             let symbol = self.next_token();
 
-            // BoolOp by itself interpreted as Literal
             if let Symbol::None = self.peek() {
+                if has_left_operand {
+                    // The BOOLOP joins the expression so far to nothing.
+                    return Err(ParseError::at_token(
+                        ParseErrorKind::MissingArgument(format!("{symbol}")),
+                        self.last_pos(),
+                    ));
+                }
+                // With no operand on either side it is an ordinary string:
+                // `test -a` is the length test of the string "-a".
                 self.literal(symbol.into_literal())?;
             } else {
                 self.boolop(symbol)?;
-                self.maybe_boolop()?;
+                self.maybe_boolop(true)?;
             }
         }
         Ok(())
diff --git a/tests/by-util/test_test.rs b/tests/by-util/test_test.rs
index c044d46076d..654ae086e14 100644
--- a/tests/by-util/test_test.rs
+++ b/tests/by-util/test_test.rs
@@ -1140,11 +1140,40 @@ fn test_filename_or_with_equal() {
 }
 
 #[test]
-#[ignore = "GNU considers this an error"]
 fn test_string_length_and_nothing() {
     new_ucmd!().args(&["-n", "a", "-a"]).fails_with_code(2);
 }
 
+#[test]
+fn test_boolop_without_right_operand() {
+    for op in ["-a", "-o"] {
+        new_ucmd!()
+            .args(&["x", op])
+            .fails_with_code(2)
+            .stderr_is(format!("test: missing argument after '{op}'\n"));
+
+        // An empty left operand is still an operand.
+        new_ucmd!().args(&["", op]).fails_with_code(2);
+
+        // Whatever precedes it, the trailing BOOLOP has nothing to join to.
+        new_ucmd!().args(&["x", "-a", "y", op]).fails_with_code(2);
+        new_ucmd!().args(&["(", "x", ")", op]).fails_with_code(2);
+        new_ucmd!().args(&["!", "x", op]).fails_with_code(2);
+    }
+}
+
+#[test]
+fn test_lone_boolop_is_a_string() {
+    // With no operand on either side, -a and -o are ordinary strings.
+    for op in ["-a", "-o"] {
+        new_ucmd!().arg(op).succeeds();
+        new_ucmd!().args(&["!", op]).fails_with_code(1);
+    }
+
+    // A unary operator still takes the BOOLOP as its operand.
+    new_ucmd!().args(&["-n", "-a"]).succeeds();
+}
+
 #[test]
 fn test_bracket_syntax_success() {
     let scenario = TestScenario::new("[");