void readLinesCheck(String vcf, int numTests) {
		Random random = new Random(20130218);

		System.out.println("Opening file '" + vcf + "'");
		FileIndexChrPos idx = new FileIndexChrPos(vcf);
		idx.setVerbose(verbose);
		idx.open();

		// Get file size
		long size = (new File(vcf)).length();
		for (int i = 1; i < numTests; i++) {
			long randPos = random.nextInt((int) size);

			// Compare methods
			LineAndPos lineSlow = idx.getLineSlow(randPos); // This method we trust
			LineAndPos line = idx.getLine(randPos); // This method we test

			// Check and show differences
			if (!line.line.equals(lineSlow.line)) {
				System.err.println("Length: " + lineSlow.line.length() + "\t" + line.line.length());
				System.err.println("Lines:\n\t" + lineSlow.line + "\n\t" + line.line);
				int shown = 0;
				for (int j = 0; j < line.line.length(); j++) {
					System.err.print(j + "\t'" + lineSlow.line.charAt(j) + "'\t'" + line.line.charAt(j) + "'");
					if (lineSlow.line.charAt(j) != line.line.charAt(j)) {
						System.err.print("\t<---");
						if (shown++ > 20) break;
					}
					System.err.println("");
				}
			}

			Assert.assertEquals(lineSlow.line, line.line);
			Assert.assertEquals(lineSlow.position, line.position);

			Gpr.showMark(i, 1);
		}

	}