private void displayHeader() {
        // Calculate width and pad with '-':
        int width = fieldWidth * tests.size() + sizeWidth;
        int dashLength = width - headline.length() - 1;
        StringBuilder head = new StringBuilder(width);
        for(int i = 0; i < dashLength / 2; i++)
            head.append('-');
        head.append(' ');
        head.append(headline);
        head.append(' ');
        for(int i = 0; i < dashLength / 2; i++)
            head.append('-');
        System.out.println(head);
        // Print column headers:
        System.out.format(sizeField, "size");
        for(Test<?> test : tests) {
            System.out.format(stringField(), test.name);
        }
        System.out.println();
    }