TestUtils: never create test directories in /tmp/

Curtis Rueden offered reluctance to fall back to creating tests in
/tmp/ when it was determined that the tests are run in in unknown
location.

This developer agrees. Therefore, let's test carefully that we found
some sensible location close to the .class files, handling unit tests
run via Maven extra nicely.

For details, see the pull request corresponding to this topic branch:
#70

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

src/main/java/org/scijava/test/TestUtils.java

@@ -103,18 +103,25 @@ public static File createTemporaryDirectory(final String prefix,
 		final Class<?> forClass, final String suffix) throws IOException
 	{
 		final URL directory = ClassUtils.getLocation(forClass);
-		if (directory != null && "file".equals(directory.getProtocol())) {
-			final String path = directory.getPath();
-			if (path != null && path.endsWith("/target/test-classes/")) {
-				final File baseDirectory =
-					new File(path.substring(0, path.length() - 13));
-				final File file = new File(baseDirectory, prefix + suffix);
-				if (file.exists()) FileUtils.deleteRecursively(file);
-				if (!file.mkdir()) throw new IOException("Could not make directory " + file);
-				return file;
-			}
+		if (directory == null) {
+			throw new IllegalArgumentException("No location for class " + forClass);
+		}
+		if (!"file".equals(directory.getProtocol())) {
+			throw new IllegalArgumentException("Invalid directory: " + directory);
 		}
-		return FileUtils.createTemporaryDirectory(prefix, suffix);
+		final String path = directory.getPath();
+		if (path == null) throw new IllegalArgumentException("Directory has null path");
+		final File baseDirectory;
+		if (path.endsWith("/target/test-classes/")) {
+			baseDirectory = new File(path).getParentFile();
+		} else {
+			baseDirectory = new File(path);
+		}
+
+		final File file = new File(baseDirectory, prefix + suffix);
+		if (file.exists()) FileUtils.deleteRecursively(file);
+		if (!file.mkdir()) throw new IOException("Could not make directory " + file);
+		return file;
 	}
 
 	/**