Add unit tests for KnownProperties (#435)

* Add unit tests for KnownProperties

Additive unit tests only - no existing test or production code changed.

Signed-off-by: vasiliy-mikhailov <vasiliy-mikhailov@users.noreply.github.com>

* Tighten JaCoCo coverage gate to match the added KnownProperties tests

INSTRUCTION 45% to 53%, COMPLEXITY 0.33 to 0.42, LINE missed 1500 to 1490; verified green (605 tests).

---------

Signed-off-by: vasiliy-mikhailov <vasiliy-mikhailov@users.noreply.github.com>

Author: vasiliy-mikhailov

pom.xml

@@ -344,17 +344,17 @@
 										<limit>
 											<counter>COMPLEXITY</counter>
 											<value>COVEREDRATIO</value>
-											<minimum>0.33</minimum>
+											<minimum>0.42</minimum>
 										</limit>
 										<limit>
 											<counter>INSTRUCTION</counter>
 											<value>COVEREDRATIO</value>
-											<minimum>45%</minimum>
+											<minimum>53%</minimum>
 										</limit>
 										<limit>
 											<counter>LINE</counter>
 											<value>MISSEDCOUNT</value>
-											<maximum>1500</maximum>
+											<maximum>1490</maximum>
 										</limit>
 									</limits>
 								</rule>

src/test/java/com/datastax/cdm/properties/KnownPropertiesTest.java

@@ -212,4 +212,51 @@ public void validateType_Boolean() {
                 KnownProperties.asType(KnownProperties.PropertyType.BOOLEAN, "false")));
     }
 
+    // ---- Tests to improve mutation coverage ----
+
+    @Test
+    public void getDefault_unknownKey() {
+        assertNull(KnownProperties.getDefault("nonexistent.key"));
+    }
+
+    @Test
+    public void getDefault_typeExistsButNoDefault() {
+        assertNull(KnownProperties.getDefault(KnownProperties.TEST_STRING_NO_DEFAULT));
+    }
+
+    @Test
+    public void getDefault_stringListNoDefault() {
+        // ORIGIN_TTL_NAMES has type STRING_LIST but no default value.
+        // If the null-check on 'value' in getDefault is bypassed (mutant),
+        // asType(STRING_LIST, null) would throw NPE via null.split(",").
+        assertNull(KnownProperties.getDefault(KnownProperties.ORIGIN_TTL_NAMES));
+    }
+
+    @Test
+    public void getDefault_numberListNoDefault() {
+        // TRANSFORM_CODECS has type STRING_LIST but no default value.
+        // Similar to above: bypassing the null check would cause NPE.
+        assertNull(KnownProperties.getDefault(KnownProperties.TRANSFORM_CODECS));
+    }
+
+    @Test
+    public void validateType_StringList_notAList() {
+        assertFalse(KnownProperties.validateType(KnownProperties.PropertyType.STRING_LIST, "not a list"));
+    }
+
+    @Test
+    public void validateType_Number_notANumber() {
+        assertFalse(KnownProperties.validateType(KnownProperties.PropertyType.NUMBER, "not a number"));
+    }
+
+    @Test
+    public void validateType_NumberList_notAList() {
+        assertFalse(KnownProperties.validateType(KnownProperties.PropertyType.NUMBER_LIST, "not a list"));
+    }
+
+    @Test
+    public void validateType_Boolean_notABoolean() {
+        assertFalse(KnownProperties.validateType(KnownProperties.PropertyType.BOOLEAN, "not a boolean"));
+    }
+
 }