trim scope selector at test token end

i.e. allow text after the assertion to not interfere with the assertion. This is how ST works when it executes the syntax tests.

examples/syntest.rs

@@ -72,16 +72,22 @@ fn get_line_assertion_details<'a>(testtoken_start: &str, testtoken_end: Option<&
         let (before_token_start, token_and_rest_of_line) = line.split_at(index);
 
         if let Some(captures) = SYNTAX_TEST_ASSERTION_PATTERN.captures(&token_and_rest_of_line[testtoken_start.len()..]) {
-            let mut sst = captures.get(3).unwrap().as_str().trim_right(); // get the scope selector text
+            let mut sst = captures.get(3).unwrap().as_str(); // get the scope selector text
+            let mut only_whitespace_after_token_end = true;
+
             if let Some(token) = testtoken_end { // if there is an end token defined in the test file header
-                sst = sst.trim_right_matches(&token); // trim it from the scope selector text
+                if let Some(end_token_pos) = sst.find(token) { // and there is an end token in the line
+                    let (ss, after_token_end) = sst.split_at(end_token_pos); // the scope selector text ends at the end token
+                    sst = &ss;
+                    only_whitespace_after_token_end = after_token_end.trim_right().is_empty();
+                }
             }
             return Some(AssertionRange {
                 begin_char: index + if captures.get(2).is_some() { testtoken_start.len() + captures.get(2).unwrap().start() } else { 0 },
                 end_char: index + if captures.get(2).is_some() { testtoken_start.len() + captures.get(2).unwrap().end() } else { 1 },
                 scope_selector_text: sst,
-                is_pure_assertion_line: before_token_start.trim_left().is_empty(), // if only whitespace precedes the test token on the line, then it is a pure assertion line
-            })
+                is_pure_assertion_line: before_token_start.trim_left().is_empty() && only_whitespace_after_token_end, // if only whitespace surrounds the test tokens on the line, then it is a pure assertion line
+            });
         }
     }
     None