implement ToolWrapper, check whether the command is working in GitWrapper

src/de/uni_passau/fim/seibt/gitwrapper/process/ToolNotWorkingException.java

+package de.uni_passau.fim.seibt.gitwrapper.process;
+
+/**
+ * An {@link Exception} indicating that a wrapped tool is not working.
+ */
+public class ToolNotWorkingException extends Exception {
+
+    public ToolNotWorkingException() {}
+
+    public ToolNotWorkingException(String message) {
+        super(message);
+    }
+
+    public ToolNotWorkingException(String message, Throwable cause) {
+        super(message, cause);
+    }
+
+    public ToolNotWorkingException(Throwable cause) {
+        super(cause);
+    }
+
+    public ToolNotWorkingException(String message, Throwable cause, boolean enableSuppression, boolean writableStackTrace) {
+        super(message, cause, enableSuppression, writableStackTrace);
+    }
+}

src/de/uni_passau/fim/seibt/gitwrapper/process/ToolWrapper.java

+package de.uni_passau.fim.seibt.gitwrapper.process;
+
+public abstract class ToolWrapper {
+
+    protected String cmd;
+
+    public ToolWrapper(String cmd) throws ToolNotWorkingException {
+        this.cmd = cmd;
+
+        if (!isWorking()) {
+            throw new ToolNotWorkingException(cmd + " is not working.");
+        }
+    }
+
+    protected abstract boolean isWorking();
+}

src/de/uni_passau/fim/seibt/gitwrapper/repo/GitWrapper.java

@@ -10,11 +10,13 @@ import java.util.regex.Pattern;
 
 import de.uni_passau.fim.seibt.gitwrapper.process.ProcessExecutor;
 import de.uni_passau.fim.seibt.gitwrapper.process.ProcessExecutor.ExecRes;
+import de.uni_passau.fim.seibt.gitwrapper.process.ToolNotWorkingException;
+import de.uni_passau.fim.seibt.gitwrapper.process.ToolWrapper;
 
 /**
  * A wrapper for executing git commands.
  */
-public class GitWrapper {
+public class GitWrapper extends ToolWrapper {
 
     public static final int EXIT_SUCCESS = 0;
     public static final int EXIT_FAIL = 1;
@@ -24,15 +26,22 @@ public class GitWrapper {
     private static final Pattern CLONING_INTO = Pattern.compile("Cloning into '(.*)'\\.\\.\\.");
     private static final Pattern ALREADY_EXISTS = Pattern.compile("fatal: destination path '(.*)' already exists and is not an empty directory\\.");
 
-    private String git;
+    private static final String GIT_VERSION_C = "--version";
+    private static final String GIT_VERSION_PREFIX = "git version";
 
     /**
      * Constructs a new {@link GitWrapper}
      *
      * @param git the git command, e.g. '/usr/bin/git' or just 'git'
      */
-    public GitWrapper(String git) {
-        this.git = git;
+    public GitWrapper(String git) throws ToolNotWorkingException {
+        super(git);
+    }
+
+    @Override
+    protected boolean isWorking() {
+        Function<ExecRes, Boolean> checkPrefix = execRes -> execRes.output.startsWith(GIT_VERSION_PREFIX);
+        return ProcessExecutor.exec(cmd, new File("."), true, GIT_VERSION_C).map(checkPrefix).orElse(false);
     }
 
     /**
@@ -124,6 +133,6 @@ public class GitWrapper {
      * @return the result of the execution
      */
     public Optional<ExecRes> exec(File workingDirectory, String... parameters) {
-        return ProcessExecutor.exec(git, workingDirectory, true, parameters);
+        return ProcessExecutor.exec(cmd, workingDirectory, true, parameters);
     }
 }