### Question:
ConstantPatternExpansionStrategy extends ExpansionStrategy { @Override public Pattern generateNullPattern(BitSet attributes) { Map<Integer, PatternEntry> allVariables = new HashMap<>(); for (int i = attributes.nextSetBit(0); i >= 0; i = attributes.nextSetBit(i + 1)) { allVariables.put(Integer.valueOf(i), new VariablePatternEntry()); } return new Pattern(allVariables); } ConstantPatternExpansionStrategy(int[][] values); static String getIdentifier(); @Override Pattern generateNullPattern(BitSet attributes); @Override List<Pattern> getChildPatterns(Pattern currentPattern);  }### Answer:
@Test public void testNullPatternGenerationSubset() { ConstantPatternExpansionStrategy out = new ConstantPatternExpansionStrategy(new int[][] {}); Pattern nullPattern = out.generateNullPattern(createAttributes(5, new int[] {2, 4})); PatternEntry[] patternEntries = nullPattern.getPatternEntries(); Assert.assertEquals(2, patternEntries.length); Assert.assertTrue(patternEntries[0] instanceof VariablePatternEntry); Assert.assertTrue(patternEntries[1] instanceof VariablePatternEntry); }
@Test public void testNullPatternGenerationAllSet() { ConstantPatternExpansionStrategy out = new ConstantPatternExpansionStrategy(new int[][] {}); Pattern nullPattern = out.generateNullPattern(createAttributes(7, new int[] {0, 1, 2, 3, 4, 5, 6})); PatternEntry[] patternEntries = nullPattern.getPatternEntries(); Assert.assertEquals(7, patternEntries.length); Assert.assertTrue(patternEntries[0] instanceof VariablePatternEntry); Assert.assertTrue(patternEntries[1] instanceof VariablePatternEntry); Assert.assertTrue(patternEntries[2] instanceof VariablePatternEntry); Assert.assertTrue(patternEntries[3] instanceof VariablePatternEntry); Assert.assertTrue(patternEntries[4] instanceof VariablePatternEntry); Assert.assertTrue(patternEntries[5] instanceof VariablePatternEntry); Assert.assertTrue(patternEntries[6] instanceof VariablePatternEntry); }
@Test public void testNullPatternGenerationNoneSet() { ConstantPatternExpansionStrategy out = new ConstantPatternExpansionStrategy(new int[][] {}); Pattern nullPattern = out.generateNullPattern(createAttributes(3, new int[] {})); PatternEntry[] patternEntries = nullPattern.getPatternEntries(); Assert.assertEquals(0, patternEntries.length); }