squeaky-clean: add task to keep only letters (exercism#2130)

emiliolg · web-flow · commit 725c4b86729f · 2022-06-19T11:22:16.000+01:00
diff --git a/exercises/concept/squeaky-clean/.docs/hints.md b/exercises/concept/squeaky-clean/.docs/hints.md
@@ -17,7 +17,11 @@
 
 - See [this method][toupper] to convert a character to upper case.
 
-## 4. Omit Greek lower case letters
+## 4. Omit characters that are not letters
+
+- See [this method][isLetter] to check if a character is a letter.
+
+## 5. Omit Greek lower case letters
 
 - `char`s support the default equality and comparison operators.
 
@@ -28,3 +32,4 @@
 [iswhitespace]: https://docs.oracle.com/en/java/javase/14/docs/api/java.base/java/lang/Character.html#isWhitespace(char)
 [iscontrol]: https://docs.oracle.com/en/java/javase/14/docs/api/java.base/java/lang/Character.html#isISOControl(char)
 [toupper]: https://docs.oracle.com/en/java/javase/14/docs/api/java.base/java/lang/Character.html#toUpperCase(char)
+[isLetter]: https://docs.oracle.com/en/java/javase/14/docs/api/java.base/java/lang/Character.html#isLetter(char)
diff --git a/exercises/concept/squeaky-clean/.docs/instructions.md b/exercises/concept/squeaky-clean/.docs/instructions.md
@@ -35,7 +35,16 @@ SqueakyClean.clean("à-ḃç");
 // => "àḂç"
 ```
 
-## 4. Omit Greek lower case letters
+## 4. Omit characters that are not letters
+
+Modify the (_static_) `SqueakyClean.clean()` method to omit any characters that are not letters.
+
+```java
+SqueakyClean.clean("a1😀2😀3😀b");
+// => "ab"
+```
+
+## 5. Omit Greek lower case letters
 
 Modify the (_static_) `SqueakyClean.clean()` method to omit any Greek letters in the range 'α' to 'ω'.
 
diff --git a/exercises/concept/squeaky-clean/src/test/java/SqueakyCleanTest.java b/exercises/concept/squeaky-clean/src/test/java/SqueakyCleanTest.java
@@ -39,6 +39,11 @@ public void string_with_no_letters() {
         assertThat(SqueakyClean.clean("\uD83D\uDE00\uD83D\uDE00\uD83D\uDE00")).isEmpty();
     }
 
+    @Test
+    public void keep_only_letters() {
+        assertThat(SqueakyClean.clean("a1\uD83D\uDE002\uD83D\uDE003\uD83D\uDE00b")).isEqualTo("ab");
+    }
+
     @Test
     public void kebab_to_camel_case() {
         assertThat(SqueakyClean.clean("à-ḃç")).isEqualTo("àḂç");
