diff --git a/src/protocol/tests/parser_validation.rs b/src/protocol/tests/parser_validation.rs
index 0462c7e1e7f81070d022ab9fa36ad21f66d6203c..7d516ce640715f9c74acc159ac56a7ed8307bef9 100644
--- a/src/protocol/tests/parser_validation.rs
+++ b/src/protocol/tests/parser_validation.rs
@@ -528,4 +528,79 @@ fn test_polymorph_array_types() {
     ).for_struct("Bar", |s| { s
         .for_field("inputs", |f| { f.assert_parser_type("in<u32>[]"); });
     });
+}
+
+#[test]
+fn test_correct_modifying_operators() {
+    // Not testing the types, just that it parses
+    Tester::new_single_source_expect_ok(
+        "valid uses",
+        "
+        func f() -> u32 {
+            auto a = 5;
+            a += 2; a -= 2; a *= 2; a /= 2; a %= 2;
+            a <<= 2; a >>= 2;
+            a |= 2; a &= 2; a ^= 2;
+            return a;
+        }
+        "
+    );
+}
+
+#[test]
+fn test_incorrect_modifying_operators() {
+    Tester::new_single_source_expect_err(
+        "wrong declaration",
+        "func f() -> u8 { auto a += 2; return a; }"
+    ).error(|e| { e.assert_msg_has(0, "expected '='"); });
+
+    Tester::new_single_source_expect_err(
+        "inside function",
+        "func f(u32 a) -> u32 { auto b = 0; auto c = f(a += 2); }"
+    ).error(|e| { e.assert_msg_has(0, "assignments are statements"); });
+
+    Tester::new_single_source_expect_err(
+        "inside tuple",
+        "func f(u32 a) -> u32 { auto b = (a += 2, a /= 2); return 0; }"
+    ).error(|e| { e.assert_msg_has(0, "assignments are statements"); });
+}
+
+#[test]
+fn test_correct_select_statement() {
+    Tester::new_single_source_expect_ok(
+        "correct single-use", "
+        primitive f() {
+            channel unused_output -> input;
+            u32 outer_value = 0;
+            sync select {
+                outer_value = get(input) -> outer_value = 0;
+                auto new_value = get(input) -> {
+                    f();
+                    outer_value = new_value;
+                }
+                get(input) + get(input) ->
+                    outer_value = 8;
+                get(input) ->
+                    {}
+                outer_value %= get(input) -> {
+                    outer_value *= outer_value;
+                    auto new_value = get(input);
+                    outer_value += new_value;
+                }
+            }
+        }
+        "
+    );
+}
+
+#[test]
+fn test_incorrect_select_statement() {
+    Tester::new_single_source_expect_err(
+        "outside sync",
+        "func f() -> u32 { select {} return 0; }"
+    ).error(|e| { e
+        .assert_num(1)
+        .assert_occurs_at(0, "select")
+        .assert_msg_has(0, "inside sync blocks");
+    });
 }
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