Add RegularExpresionTestUtil for testing regexes

src/test/java/emissary/test/util/RegularExpressionTestUtil.java

@@ -0,0 +1,81 @@
+package emissary.test.util;
+
+import org.apache.commons.collections4.CollectionUtils;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.List;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+import javax.annotation.Nullable;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
+
+/**
+ * A utility class for testing regular expressions.
+ */
+public final class RegularExpressionTestUtil {
+    private static final Logger logger = LoggerFactory.getLogger(RegularExpressionTestUtil.class);
+
+    private RegularExpressionTestUtil() {}
+
+    /**
+     * A method to test a list of values that should and should not match a particular regular expression. One of the two
+     * lists may be empty, but not both.
+     * 
+     * @param regexPatternString - Required. The string to compile into regular expression and then test against the
+     *        provided values. Must not be null or empty. Will throw a runtime exception if the regex syntax is improper.
+     * @param shouldMatch - Optional. The list of strings that should match the regular expression.
+     * @param shouldNotMatch - Optional. The list of strings that should not match the regular expression.
+     */
+    public static void testRegexPattern(String regexPatternString, @Nullable List<String> shouldMatch, @Nullable List<String> shouldNotMatch) {
+
+        if (regexPatternString == null || regexPatternString.isBlank()) {
+            fail("The test lacks required parameters.");
+        }
+
+        Pattern subjectUnderTest = Pattern.compile(regexPatternString);
+
+        testRegexPattern(subjectUnderTest, shouldMatch, shouldNotMatch);
+
+    }
+
+    /**
+     * A method to test a list of values that should and should not match a particular regular expression. One of the two
+     * lists may be empty or null, but not both.
+     * 
+     * @param patternUnderTest Required. The pre-compiled pattern used to test against the provided values. Must not be
+     *        null.
+     * @param shouldMatch Optional. The list of strings that should match the regular expression.
+     * @param shouldNotMatch Optional. The list of strings that should not match the regular expression.
+     */
+    public static void testRegexPattern(Pattern patternUnderTest, @Nullable List<String> shouldMatch, @Nullable List<String> shouldNotMatch) {
+        int fineGrainTestCount = 0;
+        if (patternUnderTest == null || (CollectionUtils.isEmpty(shouldMatch) && CollectionUtils.isEmpty(shouldNotMatch))) {
+            fail("The test lacks required parameters.");
+        }
+
+        if (!CollectionUtils.isEmpty(shouldMatch)) {
+            for (String matchMe : shouldMatch) {
+                Matcher mm = patternUnderTest.matcher(matchMe);
+                assertTrue(mm.find(), String.format(" -- Pattern SHOULD match the regex [%s], but did not: %s", patternUnderTest.pattern(), matchMe));
+                fineGrainTestCount++;
+            }
+        }
+
+        if (!CollectionUtils.isEmpty(shouldNotMatch)) {
+            for (String dontMatchMe : shouldNotMatch) {
+                Matcher dmm = patternUnderTest.matcher(dontMatchMe);
+                assertFalse(dmm.find(),
+                        String.format(" -- Pattern SHOULD NOT match the regex[%s], but did: %s", patternUnderTest.pattern(), dontMatchMe));
+                fineGrainTestCount++;
+            }
+        }
+        assertTrue(fineGrainTestCount > 0, "No regex assertions performed.");
+        logger.debug("Successfully asserted {} regex test cases.", fineGrainTestCount);
+    }
+
+
+}