wordy 1.3.0: Reject syntax errors

I unfortunately considered the existing example solution not quite up to
the task of doing this, so I was forced to write a new implementation
from scratch.

exercism/problem-specifications#1383

Author: petertseng

exercises/wordy/Cargo.toml

@@ -1,3 +1,3 @@
 [package]
 name = "wordy"
-version = "1.2.0"
+version = "1.3.0"

exercises/wordy/README.md

@@ -43,6 +43,14 @@ left-to-right, _ignoring the typical order of operations._
 
 15  (i.e. not 9)
 
+## Iteration 4 — Errors
+
+The parser should reject:
+
+* Unsupported operations ("What is 52 cubed?")
+* Non-math questions ("Who is the President of the United States")
+* Word problems with invalid syntax ("What is 1 plus plus 2?")
+
 ## Bonus — Exponentials
 
 If you'd like, handle exponentials.

exercises/wordy/tests/wordy.rs

@@ -112,3 +112,38 @@ fn non_math_question() {
     let command = "Who is the President of the United States?";
     assert!(answer(command).is_none());
 }
+
+#[test]
+#[ignore]
+fn reject_incomplete_problem() {
+    let command = "What is 1 plus?";
+    assert!(answer(command).is_none());
+}
+
+#[test]
+#[ignore]
+fn reject_two_operations_in_a_row() {
+    let command = "What is 1 plus plus 2?";
+    assert!(answer(command).is_none());
+}
+
+#[test]
+#[ignore]
+fn reject_two_numbers_in_a_row() {
+    let command = "What is 1 plus 2 1?";
+    assert!(answer(command).is_none());
+}
+
+#[test]
+#[ignore]
+fn reject_postfix_notation() {
+    let command = "What is 1 2 plus?";
+    assert!(answer(command).is_none());
+}
+
+#[test]
+#[ignore]
+fn reject_prefix_notation() {
+    let command = "What is plus 1 2?";
+    assert!(answer(command).is_none());
+}