java: grade-school tests and example implementation

assignments/java/grade-school/example.java

+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.TreeSet;
+
+public class School {
+
+  private final Map<Integer, Set<String>> database = new HashMap<Integer, Set<String>>();
+
+  public Map<Integer, Set<String>> db() {
+    // Leaks internal storage to caller
+    return database;
+  }
+
+  public void add(String student, int grade) {
+    Set<String> students = grade(grade);
+    students.add(student);
+  }
+
+  public Set<String> grade(int grade) {
+    // Leaks internal storage to caller
+    if (!database.containsKey(grade)) {
+      database.put(grade, new TreeSet<String>());
+    }
+    return database.get(grade);
+  }
+
+  public Map<Integer, List<String>> sort() {
+    Map<Integer, List<String>> sortedStudents = new HashMap<Integer, List<String>>();
+    for (Integer grade : database.keySet()) {
+      // Relies on using a TreeSet internally
+      List<String> sortedGrade = new ArrayList<String>(database.get(grade));
+      sortedStudents.put(grade, sortedGrade);
+    }
+    return sortedStudents;
+  }
+}

assignments/java/grade-school/src/test/java/SchoolTest.java

+import static org.fest.assertions.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+public class SchoolTest {
+  private final School school = new School();
+
+  @Test
+  public void startsWithNoStudents() {
+    assertThat(school.db()).isEmpty();
+  }
+
+  @Test
+  public void addsStudents() {
+    school.add("Aimee", 2);
+    assertThat(school.db().get(2)).contains("Aimee");
+  }
+
+  @Test
+  public void addsMoreStudentsInSameGrade() {
+    final int grade = 2;
+    school.add("James", grade);
+    school.add("Blair", grade);
+    school.add("Paul", grade);
+
+    assertThat(school.db().get(grade)).hasSize(3).contains("James", "Blair", "Paul");
+  }
+
+  @Test
+  public void addsStudentsInMultipleGrades() {
+    school.add("Chelsea", 3);
+    school.add("Logan", 7);
+
+    assertThat(school.db()).hasSize(2);
+    assertThat(school.db().get(3)).hasSize(1).contains("Chelsea");
+    assertThat(school.db().get(7)).hasSize(1).contains("Logan");
+  }
+
+  @Test
+  public void getsStudentsInAGrade() {
+    school.add("Franklin", 5);
+    school.add("Bradley", 5);
+    school.add("Jeff", 1);
+    assertThat(school.grade(5)).hasSize(2).contains("Franklin", "Bradley");
+  }
+
+  @Test
+  public void getsStudentsInEmptyGrade() {
+    assertThat(school.grade(1)).isEmpty();
+  }
+
+  @Test
+  public void sortsSchool() {
+    school.add("Jennifer", 4);
+    school.add("Kareem", 6);
+    school.add("Christopher", 4);
+    school.add("Kyle", 3);
+    Map<Integer, List<String>> sortedStudents = new HashMap<Integer, List<String>>();
+    sortedStudents.put(6, Arrays.asList("Kareem"));
+    sortedStudents.put(4, Arrays.asList("Christopher", "Jennifer"));
+    sortedStudents.put(3, Arrays.asList("Kyle"));
+
+    assertThat(school.sort()).isEqualTo(sortedStudents);
+  }
+}