Added tests for the cause tag

src/main/java/net/thauvin/erik/httpstatus/taglibs/CauseTag.java

@@ -52,15 +52,24 @@ public class CauseTag extends XmlSupport {
     @Override
     public void doTag() throws IOException {
         final PageContext pageContext = (PageContext) getJspContext();
-        @SuppressWarnings("PMD.CloseResource") final JspWriter out = pageContext.getOut();
+        final JspWriter out = pageContext.getOut();
 
         final Throwable cause = pageContext.getErrorData().getThrowable().getCause();
 
-        String message = defaultValue;
-        if (cause != null && cause.getLocalizedMessage() != null) {
-            message = cause.getLocalizedMessage();
-        }
+        Utils.outWrite(out, getCause(cause), defaultValue, escapeXml);
+    }
 
-        Utils.outWrite(out, message, defaultValue, escapeXml);
+    /**
+     * Returns the cause's localized message or default value.
+     *
+     * @param cause The cause.
+     * @return The cause or {@code null}.
+     */
+    public String getCause(Throwable cause) {
+        if (cause != null && cause.getLocalizedMessage() != null) {
+            return cause.getLocalizedMessage();
+        } else {
+            return null;
+        }
     }
 }

src/test/java/net/thauvin/erik/httpstatus/CauseTagTest.java

@@ -0,0 +1,57 @@
+/*
+ * CauseTagTest.java
+ *
+ * Copyright 2023 sErik C. Thauvin (erik@thauvin.net)
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   Redistributions of source code must retain the above copyright notice, this
+ *   list of conditions and the following disclaimer.
+ *
+ *   Redistributions in binary form must reproduce the above copyright notice,
+ *   this list of conditions and the following disclaimer in the documentation
+ *   and/or other materials provided with the distribution.
+ *
+ *   Neither the name of this project nor the names of its contributors may be
+ *   used to endorse or promote products derived from this software without
+ *   specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package net.thauvin.erik.httpstatus;
+
+import net.thauvin.erik.httpstatus.taglibs.CauseTag;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Implements the CauseTagTest class.
+ *
+ * @author <a href="https://erik.thauvin.net/">Erik C. Thauvin</a>
+ * @since 1.0
+ */
+class CauseTagTest {
+    @Test
+    void causeTest() {
+        var message = "This is the cause";
+        var tag = new CauseTag();
+
+        assertThat(tag.getCause(new Exception(message))).as("has cause").isEqualTo(message);
+        assertThat(tag.getCause(new Exception())).as("no cause").isNull();
+        assertThat(tag.getCause(null)).as("null").isNull();
+        assertThat(tag.getCause(new Exception(""))).as("empty").isEmpty();
+    }
+}