Understandable error message if a formatter needs output location. Closes #148, #232, #269.

Author: aslakhellesoy

History.md

@@ -1,6 +1,7 @@
 ## [Git master](https://github.com/cucumber/cucumber-jvm/compare/v1.0.0.RC23...master)
 
-* [JUnit] Running with JUnit uses a null formatter by default (instead of a progress formatter). Aslak Hellesøy.
+* [Core] Understandable error message if a formatter needs output location. ([#148](https://github.com/cucumber/cucumber-jvm/issues/148), [#232](https://github.com/cucumber/cucumber-jvm/issues/232), [#269](https://github.com/cucumber/cucumber-jvm/issues/269) Aslak Hellesøy)
+* [JUnit] Running with JUnit uses a null formatter by default (instead of a progress formatter). (Aslak Hellesøy)
 * [Clojure] Fix release artifacts so cucumber-clojure can be released. ([#270](https://github.com/cucumber/cucumber-jvm/issues/270) Aslak Hellesøy)
 * [Java] The @Pending annotation no longer exists. Throw a PendingException instead ([#271](https://github.com/cucumber/cucumber-jvm/issues/271) Aslak Hellesøy)
 

core/src/main/java/cucumber/formatter/FormatterConverter.java

@@ -45,19 +45,17 @@ public Formatter convert(String formatterString) {
         }
         Class<? extends Formatter> formatterClass = formatterClass(formatterName);
         try {
-            return instantiate(formatterClass, ctorArg);
+            return instantiate(formatterString, formatterClass, ctorArg);
         } catch (IOException e) {
             throw new CucumberException(e);
         }
     }
 
-    private Formatter instantiate(Class<? extends Formatter> formatterClass, Object ctorArg) throws IOException {
-        Constructor<? extends Formatter> constructor;
-
+    private Formatter instantiate(String formatterString, Class<? extends Formatter> formatterClass, Object ctorArg) throws IOException {
         for (Class ctorArgClass : CTOR_ARGS) {
-            constructor = findConstructor(formatterClass, ctorArgClass);
+            Constructor<? extends Formatter> constructor = findConstructor(formatterClass, ctorArgClass);
             if (constructor != null) {
-                ctorArg = convert(ctorArg, ctorArgClass);
+                ctorArg = convertOrNull(ctorArg, ctorArgClass);
                 if (ctorArg != null) {
                     try {
                         return constructor.newInstance(ctorArg);
@@ -71,10 +69,13 @@ private Formatter instantiate(Class<? extends Formatter> formatterClass, Object
                 }
             }
         }
+        if (ctorArg == null) {
+            throw new CucumberException(String.format("You must supply an output argument to %s. Like so: %s:output", formatterString, formatterString));
+        }
         throw new CucumberException(String.format("%s must have a single-argument constructor that takes one of the following: %s", formatterClass, asList(CTOR_ARGS)));
     }
 
-    private Object convert(Object ctorArg, Class ctorArgClass) throws IOException {
+    private Object convertOrNull(Object ctorArg, Class ctorArgClass) throws IOException {
         if (ctorArgClass.isAssignableFrom(ctorArg.getClass())) {
             return ctorArg;
         }

core/src/test/java/cucumber/formatter/FormatterConverterTest.java

@@ -1,5 +1,6 @@
 package cucumber.formatter;
 
+import cucumber.runtime.CucumberException;
 import gherkin.formatter.Formatter;
 import org.junit.Test;
 
@@ -8,6 +9,7 @@
 import static cucumber.formatter.TempDir.createTempDirectory;
 import static cucumber.formatter.TempDir.createTempFile;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
 
 public class FormatterConverterTest {
     private FormatterConverter fc = new FormatterConverter();
@@ -24,6 +26,16 @@ public void instantiates_html_formatter_with_dir_arg() throws IOException {
         assertEquals(HTMLFormatter.class, formatter.getClass());
     }
 
+    @Test
+    public void fails_to_instantiate_html_formatter_without_dir_arg() throws IOException {
+        try {
+            fc.convert("html");
+            fail();            
+        } catch(CucumberException e) {
+            assertEquals("You must supply an output argument to html. Like so: html:output", e.getMessage());
+        }
+    }
+
     @Test
     public void instantiates_pretty_formatter_with_file_arg() throws IOException {
         Formatter formatter = fc.convert("pretty:" + createTempFile().getAbsolutePath());