add some basic tests (mainly copied from GitCommitIdMojoIntegrationTest but adjusted to the core-plugin)

Author: TheSnoozer

pom.xml

@@ -231,6 +231,12 @@
             <version>1.1.1</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>com.github.stefanbirkner</groupId>
+            <artifactId>system-rules</artifactId>
+            <version>1.19.0</version>
+            <scope>test</scope>
+        </dependency>
         <!-- slf4j is a dependency of jgit, this suppresses slf4j's warning during testing when we mock jgit stuff -->
         <dependency>
             <groupId>org.slf4j</groupId>

src/test/java/pl/project13/core/AvailableGitTestRepo.java

@@ -0,0 +1,92 @@
+/*
+ * This file is part of git-commit-id-plugin-core by Konrad 'ktoso' Malawski <konrad.malawski@java.pl>
+ *
+ * git-commit-id-plugin-core is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * git-commit-id-plugin-core is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with git-commit-id-plugin-core.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package pl.project13.core;
+
+
+import javax.annotation.Nonnull;
+import java.io.File;
+
+public enum AvailableGitTestRepo {
+  WITH_ONE_COMMIT("src/test/resources/_git_one_commit"),
+  WITH_ONE_COMMIT_DIRTY("src/test/resources/_git_one_commit_dirty"),
+  GIT_COMMIT_ID("src/test/resources/_git_of_git_commit_id"),
+  GIT_WITH_NO_CHANGES("src/test/resources/_git_with_no_changes"),
+  ON_A_TAG("src/test/resources/_git_on_a_tag"),
+  /**
+   * <pre>
+   * $ lg
+   *   * b6a73ed - (HEAD, master) third addition (32 hours ago) <p>Konrad Malawski</p>
+   *   * d37a598 - (newest-tag, lightweight-tag) second line (32 hours ago) <p>Konrad Malawski</p>
+   *   * 9597545 - (annotated-tag) initial commit (32 hours ago) <p>Konrad Malawski</p>
+   * </pre>
+   *
+   * Where the <b>newest-tag</b> was created latest:
+   * <pre>
+   * $ tag -v newest-tag
+   * object d37a598a7a98531ad1375966642c6b1263129436
+   * tagger Konrad Malawski <p>konrad.malawski@project13.pl</p> 1346017608 +0200
+   *
+   * $ tag -v annotated-tag
+   * object 95975455ef2b1af048f2926b9ba7fb804e22171b
+   * tagger Konrad Malawski <p>konrad.malawski@project13.pl</p> 1345901561 +0200
+   * </pre>
+   */
+  WITH_COMMIT_THAT_HAS_TWO_TAGS("src/test/resources/_git_with_commit_that_has_two_tags"),
+  ON_A_TAG_DIRTY("src/test/resources/_git_on_a_tag_dirty"),
+  WITH_SUBMODULES("src/test/resources/_git_with_submodules"),
+  /**
+   * <pre>
+   * b6a73ed - (HEAD, master) third addition (4 minutes ago) <p>Konrad Malawski</p>
+   * d37a598 - (lightweight-tag) second line (6 minutes ago) <p>Konrad Malawski</p>
+   * 9597545 - (annotated-tag) initial commit (6 minutes ago) <p>Konrad Malawski</p>
+   * </pre>
+   */
+  WITH_LIGHTWEIGHT_TAG_BEFORE_ANNOTATED_TAG("src/test/resources/_git_lightweight_tag_before_annotated_tag"),
+  /**
+   * <pre>
+   * * 9cb810e - Change in tag - Fri, 29 Nov 2013 10:39:31 +0100 (tag: test_tag, branch: test)
+   * | * 2343428 - Moved master - Fri, 29 Nov 2013 10:38:34 +0100 (HEAD, branch: master)
+   * |/
+   * * e3d159d - Added readme - Fri, 29 Nov 2013 10:38:02 +0100
+   * </pre>
+   */
+  WITH_TAG_ON_DIFFERENT_BRANCH("src/test/resources/_git_with_tag_on_different_branch"),
+  WITH_ONE_COMMIT_WITH_SPECIAL_CHARACTERS("src/test/resources/_git_one_commit_with_umlaut"),
+  /**
+    * <pre>
+    * b0c6d28b3b83bf7b905321bae67d9ca4c75a203f 2015-06-04 00:50:18 +0200  (HEAD, master)
+    * 0e3495783c56589213ee5f2ae8900e2dc1b776c4 2015-06-03 23:59:10 +0200  (tag: v2.0)
+    * f830b5f85cad3d33ba50d04c3d1454e1ae469057 2015-06-03 23:57:53 +0200  (tag: v1.0)
+    * </pre>
+    */
+  WITH_THREE_COMMITS_AND_TWO_TAGS_CURRENTLY_ON_COMMIT_WITHOUT_TAG("src/test/resources/_git_three_commits_and_two_tags_currently_on_commit_without_tag"),
+  // TODO: Why do the tests get stuck when we use .git??
+  MAVEN_GIT_COMMIT_ID_PLUGIN("src/test/resources/_git_one_commit_with_umlaut")
+  ;
+
+  private String dir;
+
+  AvailableGitTestRepo(String dir) {
+    this.dir = dir;
+  }
+
+  @Nonnull
+  public File getDir() {
+    return new File(dir);
+  }
+}