Add terminal history class

src/terminal/TerminalHistory.java

@@ -0,0 +1,42 @@
+package terminal;
+
+import java.util.*;
+
+public class TerminalHistory {
+
+    private List<String> history;
+    private int currentLineIndex;
+
+    public TerminalHistory() {
+        this.history = new ArrayList<>();
+        this.currentLineIndex = 0;
+    }
+
+    public void addLine(String line) {
+        history.add(line);
+        currentLineIndex = history.size();
+    }
+
+    public String getPreviousLine() {
+        if (isBeginning())
+            return null;
+        
+        return history.get(--currentLineIndex);
+    }
+
+    private boolean isBeginning() {
+        return currentLineIndex == 0;
+    }
+
+    public String getNextLine() {
+        if (isEnd())
+            return null;
+
+        return history.get(++currentLineIndex);
+    }
+
+    private boolean isEnd() {
+        return currentLineIndex >= history.size() - 1;
+    }
+
+}

test/terminal/TerminalHistoryTest.java

@@ -0,0 +1,103 @@
+package terminal;
+
+import static org.junit.Assert.*;
+
+import org.junit.*;
+
+public class TerminalHistoryTest {
+
+    private TerminalHistory history;
+
+    private void assertAtBeginning() {
+        assertNull(history.getPreviousLine());
+    }
+
+    private void assertAtEnd() {
+        assertNull(history.getNextLine());
+    }
+
+    private void assertPrevious(String expected) {
+        assertEquals(expected, history.getPreviousLine());
+    }
+
+    private void assertNext(String expected) {
+        assertEquals(expected, history.getNextLine());
+    }
+
+    @Before
+    public void setUp() {
+        history = new TerminalHistory();
+    }
+
+    @After
+    public void tearDown() {}
+
+    @Test
+    public void historyStartsWithNoLines() {
+        assertAtBeginning();
+        assertAtEnd();
+    }
+
+    @Test
+    public void addOneLineToHistory() {
+        history.addLine("test line");
+
+        assertPrevious("test line");
+        assertAtBeginning();
+        assertAtEnd();
+    }
+
+    @Test
+    public void moveBackwards() {
+        history.addLine("one");
+        history.addLine("two");
+
+        assertPrevious("two");
+        assertPrevious("one");
+        assertAtBeginning();
+    }
+
+    @Test
+    public void moveForwards() {
+        history.addLine("one");
+        history.addLine("two");
+        history.getPreviousLine();
+        history.getPreviousLine();
+
+        assertNext("two");
+        assertAtEnd();
+    }
+
+    @Test
+    public void moveBackAndForth() {
+        history.addLine("one");
+        history.addLine("two");
+
+        assertAtEnd();
+        assertPrevious("two");
+        assertAtEnd();
+        assertPrevious("one");
+        assertAtBeginning();
+        assertNext("two");
+        assertAtEnd();
+        assertPrevious("one");
+        assertAtBeginning();
+        assertNext("two");
+        assertAtEnd();
+    }
+
+    @Test
+    public void addedLineGoesAtEndOfHistory() {
+        history.addLine("one");
+        history.addLine("two");
+        history.getPreviousLine();
+        history.getPreviousLine();
+        history.addLine("three");
+
+        assertPrevious("three");
+        assertPrevious("two");
+        assertPrevious("one");
+        assertAtBeginning();
+    }
+
+}