fix: add tests

build.gradle

@@ -1,4 +1,5 @@
 plugins {
+    id 'groovy'
     id 'java-gradle-plugin'
     id 'maven-publish'
     id 'com.widen.versioning' version '0.1.0'
@@ -34,13 +35,16 @@ publishing {
 
 dependencies {
     compile 'commons-io:commons-io:2.6'
+
+    testCompile 'org.codehaus.groovy:groovy-all:2.4.12'
+    testCompile 'org.spockframework:spock-core:1.1-groovy-2.4'
 }
 
 gradlePlugin {
     plugins {
         versioning {
-            id = "com.widen.versioning"
-            implementationClass = "com.widen.versioning.VersioningPlugin"
+            id = 'com.widen.versioning'
+            implementationClass = 'com.widen.versioning.VersioningPlugin'
         }
     }
 }

src/main/java/com/widen/versioning/VersionGenerator.java

@@ -22,6 +22,9 @@ public static String generateFromGit() {
     }
 
     public static String generateFromString(String describe) {
+        if (describe == null) {
+            return "";
+        }
         return describe.replaceFirst("-", "+");
     }
 }

src/test/groovy/com/widen/versioning/VersionGeneratorTest.groovy

@@ -0,0 +1,18 @@
+package com.widen.versioning
+
+import spock.lang.Specification
+import spock.lang.Unroll
+
+class VersionGeneratorTest extends Specification {
+    @Unroll("git describe '#describe' should become '#version'")
+    def "parse git describe to version"() {
+        expect:
+        VersionGenerator.generateFromString(describe) == version
+
+        where:
+        describe           | version
+        null               | ""
+        ""                 | ""
+        "0.1.0-4-ge7426f0" | "0.1.0+4-ge7426f0"
+    }
+}