added validation to make sure max tries value is valid

Author: elennick

src/main/java/com/evanlennick/retry4j/config/RetryConfigBuilder.java

@@ -36,6 +36,8 @@ public class RetryConfigBuilder {
             = "Number of tries can only be specified once!";
     public final static String CAN_ONLY_SPECIFY_CUSTOM_EXCEPTION_STRAT__ERROR_MSG
             = "You cannot use built in exception logic and custom exception logic in the same config!";
+    public final static String MUST_SPECIFY_MAX_TRIES_ABOVE_0__ERROR_MSG
+            = "Cannot specify a maximum number of tries less than 1!";
 
     public RetryConfigBuilder() {
         this.config = new RetryConfig();
@@ -110,6 +112,10 @@ public RetryConfigBuilder retryOnCustomExceptionLogic(Function<Exception, Boolea
     }
 
     public RetryConfigBuilder withMaxNumberOfTries(int max) {
+        if (max < 1) {
+            throw new InvalidRetryConfigException(MUST_SPECIFY_MAX_TRIES_ABOVE_0__ERROR_MSG);
+        }
+
         if (config.getMaxNumberOfTries() != null) {
             throw new InvalidRetryConfigException(ALREADY_SPECIFIED_NUMBER_OF_TRIES__ERROR_MSG);
         }

src/test/java/com/evanlennick/retry4j/config/RetryConfigBuilderTest_WithValidationTest.java

@@ -130,6 +130,21 @@ public void verifyNoMaxTriesThrowsException() {
         }
     }
 
+    @Test
+    public void verifyZeroMaxTriesThrowsException() {
+        try {
+            retryConfigBuilder
+                    .withDelayBetweenTries(1, ChronoUnit.SECONDS)
+                    .withExponentialBackoff()
+                    .withMaxNumberOfTries(0)
+                    .build();
+            fail("Expected InvalidRetryConfigException but one wasn't thrown!");
+        } catch (InvalidRetryConfigException e) {
+            assertThat(e.getMessage())
+                    .isEqualTo(RetryConfigBuilder.MUST_SPECIFY_MAX_TRIES_ABOVE_0__ERROR_MSG);
+        }
+    }
+
     @Test
     public void verifyTwoExceptionStrategiesThrowsException_anyAndSpecific() {
         try {