Issue #58: added some code coverage for Main

pom.xml

@@ -66,6 +66,12 @@
             <version>4.12</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>com.github.stefanbirkner</groupId>
+            <artifactId>system-rules</artifactId>
+            <version>1.16.1</version>
+            <scope>test</scope>
+        </dependency>
         <dependency>
             <groupId>org.powermock</groupId>
             <artifactId>powermock-api-mockito</artifactId>
@@ -442,8 +448,8 @@
                                 <regexes>
                                     <regex>
                                         <pattern>com.github.checkstyle.regression.Main</pattern>
-                                        <branchRate>0</branchRate>
-                                        <lineRate>0</lineRate>
+                                        <branchRate>75</branchRate>
+                                        <lineRate>77</lineRate>
                                     </regex>
                                     <regex>
                                         <pattern>com.github.checkstyle.regression.configuration.ConfigGenerator</pattern>

src/main/java/com/github/checkstyle/regression/Main.java

@@ -79,7 +79,7 @@ private Main() {
      * @param args the CLI arguments
      * @throws Exception execute failure
      */
-    public static void main(String[] args) throws Exception {
+    public static void main(String... args) throws Exception {
         final Options options = createOptions();
         final CommandLineParser parser = new DefaultParser();
         final HelpFormatter formatter = new HelpFormatter();
@@ -96,7 +96,7 @@ public static void main(String[] args) throws Exception {
         catch (ParseException ex) {
             System.err.println(ex.getMessage());
             formatter.printHelp("java -jar regression-tool.jar", options, true);
-            System.exit(1);
+            System.exit(-1);
         }
 
         final Arguments arguments = ImmutableArguments.builder()

src/test/java/com/github/checkstyle/regression/MainTest.java

@@ -0,0 +1,157 @@
+////////////////////////////////////////////////////////////////////////////////
+// checkstyle: Checks Java source code for adherence to a set of rules.
+// Copyright (C) 2001-2017 the original author or authors.
+//
+// This library 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 2.1 of the License, or (at your option) any later version.
+//
+// This library 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
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+////////////////////////////////////////////////////////////////////////////////
+
+package com.github.checkstyle.regression;
+
+import static com.github.checkstyle.regression.internal.TestUtils.assertUtilsClassHasPrivateConstructor;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+import java.io.File;
+import java.util.Locale;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.contrib.java.lang.system.ExpectedSystemExit;
+import org.junit.contrib.java.lang.system.SystemErrRule;
+import org.junit.contrib.java.lang.system.SystemOutRule;
+import org.junit.rules.TemporaryFolder;
+
+public final class MainTest {
+    private static final String USAGE = String.format(Locale.ROOT,
+            "usage: java -jar regression-tool.jar -r <arg> -p <arg> [-t <arg>]%n"
+                    + "       [--stopAfterConfigGeneration]%n"
+                    + " -r,--checkstyleRepoPath <arg>     the path of the checkstyle repository%n"
+                    + " -p,--patchBranch <arg>            the name of the PR branch%n"
+                    + " -t,--checkstyleTesterPath <arg>   the path of the checkstyle-tester%n"
+                    + "                                   directory%n"
+                    + "    --stopAfterConfigGeneration    indicates that regression tool would%n"
+                    + "                                   stop after generating config%n");
+
+    private static final String EOL = System.getProperty("line.separator");
+
+    @Rule
+    public final TemporaryFolder temporaryFolder = new TemporaryFolder();
+    @Rule
+    public final ExpectedSystemExit exit = ExpectedSystemExit.none();
+    @Rule
+    public final SystemErrRule systemErr = new SystemErrRule().enableLog().mute();
+    @Rule
+    public final SystemOutRule systemOut = new SystemOutRule().enableLog().mute();
+
+    @Test
+    public void testIsProperUtilsClass() throws Exception {
+        assertUtilsClassHasPrivateConstructor(Main.class);
+    }
+
+    @Test
+    public void testNoArguments() throws Exception {
+        exit.expectSystemExitWithStatus(-1);
+        exit.checkAssertionAfterwards(() -> {
+            assertEquals("Unexpected ouput log", USAGE, systemOut.getLog());
+            assertEquals("Unexpected system error log", "Missing required options: r, p" + EOL,
+                    systemErr.getLog());
+        });
+        Main.main();
+    }
+
+    @Test
+    public void testRepoNonExistent() throws Exception {
+        try {
+            Main.main("-r", "BAD", "-p", "BAD");
+            fail("Exception is expected");
+        }
+        catch (IllegalArgumentException ex) {
+            assertEquals("Invalid error message",
+                    "path of local git repo must exist and be a directory",
+                    ex.getLocalizedMessage());
+        }
+    }
+
+    @Test
+    public void testRepoEmpty() throws Exception {
+        try {
+            Main.main("-r", "", "-p", "BAD");
+            fail("Exception is expected");
+        }
+        catch (IllegalArgumentException ex) {
+            assertEquals("Invalid error message",
+                    "path of local git repo must exist and be a directory",
+                    ex.getLocalizedMessage());
+        }
+    }
+
+    @Test
+    public void testRepoFile() throws Exception {
+        try {
+            final File file = temporaryFolder.newFile();
+            Main.main("-r", file.getCanonicalPath(), "-p", "BAD");
+            fail("Exception is expected");
+        }
+        catch (IllegalArgumentException ex) {
+            assertEquals("Invalid error message",
+                    "path of local git repo must exist and be a directory",
+                    ex.getLocalizedMessage());
+        }
+    }
+
+    @Test
+    public void testMissingTester() throws Exception {
+        try {
+            final File directory = temporaryFolder.newFolder();
+            Main.main("-r", directory.getCanonicalPath(), "-p", "BAD");
+            fail("Exception is expected");
+        }
+        catch (IllegalArgumentException ex) {
+            assertEquals("Invalid error message",
+                    "missing checkstyleTesterPath, which is required if you are not using"
+                            + " --stopAfterConfigGeneration mode", ex.getLocalizedMessage());
+        }
+    }
+
+    @Test
+    public void testTesterNonExistent() throws Exception {
+        try {
+            final File directory = temporaryFolder.newFolder();
+            Main.main("-r", directory.getCanonicalPath(), "-t", "BAD", "-p", "BAD");
+            fail("Exception is expected");
+        }
+        catch (IllegalArgumentException ex) {
+            assertEquals("Invalid error message",
+                    "path of checkstyle tester must exist and be a directory",
+                    ex.getLocalizedMessage());
+        }
+    }
+
+    @Test
+    public void testTesterFile() throws Exception {
+        try {
+            final File directory = temporaryFolder.newFolder();
+            final File file = temporaryFolder.newFile();
+            Main.main("-r", directory.getCanonicalPath(), "-t", file.getCanonicalPath(), "-p",
+                    "BAD");
+            fail("Exception is expected");
+        }
+        catch (IllegalArgumentException ex) {
+            assertEquals("Invalid error message",
+                    "path of checkstyle tester must exist and be a directory",
+                    ex.getLocalizedMessage());
+        }
+    }
+}