Refactoring Main to be more testable

Added tests for AgeGuesserUI as well.

src/main/java/com/dacklabs/ageguesser/AgeGuesserUI.java

@@ -0,0 +1,32 @@
+package com.dacklabs.ageguesser;
+
+public class AgeGuesserUI {
+    private final ConsoleIO io;
+    private final AgeGuesser guesser;
+
+    public AgeGuesserUI(ConsoleIO io, AgeGuesser guesser) {
+        this.io = io;
+        this.guesser = guesser;
+    }
+
+    public void start() {
+        io.printLine("I will guess your age, and you tell me if it was higher, lower, or yes.");
+        boolean correct = false;
+        while (!correct) {
+            int guess = guesser.guess();
+            io.printLine(String.format("Are you %d years old? (possible answers: higher, lower, yes)", guess));
+            String answer = io.getUserInput().toLowerCase();
+
+            if (answer.contains("higher")) {
+                guesser.addHint(HintDirection.HIGHER);
+            } else if (answer.contains("lower")) {
+                guesser.addHint(HintDirection.LOWER);
+            } else if (answer.contains("yes")) {
+                correct = true;
+            } else {
+                io.printLine(String.format("I didn't understand \"%s\". Try again", answer));
+            }
+        }
+        io.printLine(String.format("Hooray! I only needed %d hints!", guesser.hintsReceived()));
+    }
+}

src/main/java/com/dacklabs/ageguesser/ConsoleIO.java

@@ -0,0 +1,7 @@
+package com.dacklabs.ageguesser;
+
+public interface ConsoleIO {
+    String getUserInput();
+
+    void printLine(String line);
+}

src/main/java/com/dacklabs/ageguesser/Main.java

@@ -1,32 +1,8 @@
 package com.dacklabs.ageguesser;
 
-import java.util.Scanner;
-
-import static com.dacklabs.ageguesser.HintDirection.HIGHER;
-import static com.dacklabs.ageguesser.HintDirection.LOWER;
-
 public class Main {
     public static void main(String[] args) {
-        Scanner scanner = new Scanner(System.in);
-
-        System.out.println("I will guess your age, and you tell me if it was higher, lower, or correct.");
-        AgeGuesser guesser = new AgeGuesser();
-        boolean correct = false;
-        while (!correct) {
-            int guess = guesser.guess();
-            System.out.println(String.format("Are you %d years old? (possible answers: higher, lower, correct)", guess));
-            String answer = scanner.nextLine().toLowerCase();
-
-            if (answer.contains("higher")) {
-                guesser.addHint(HIGHER);
-            } else if (answer.contains("lower")) {
-                guesser.addHint(LOWER);
-            } else if (answer.contains("correct")) {
-                correct = true;
-            } else {
-                System.out.println(String.format("I didn't understand \"%s\". Try again", answer));
-            }
-        }
-        System.out.println(String.format("Hooray! I only needed %d hints!", guesser.hintsReceived()));
+        AgeGuesserUI ui = new AgeGuesserUI(new SysIO(), new AgeGuesser());
+        ui.start();
     }
 }

src/main/java/com/dacklabs/ageguesser/SysIO.java

@@ -0,0 +1,18 @@
+package com.dacklabs.ageguesser;
+
+import java.util.Scanner;
+
+public final class SysIO implements ConsoleIO {
+
+    private final Scanner scanner = new Scanner(System.in);
+
+    @Override
+    public String getUserInput() {
+        return scanner.nextLine();
+    }
+
+    @Override
+    public void printLine(String line) {
+        System.out.println(line);
+    }
+}

src/test/java/com/dacklabs/ageguesser/AgeGuesserUITest.java

@@ -0,0 +1,66 @@
+package com.dacklabs.ageguesser;
+
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class AgeGuesserUITest {
+
+    @Test
+    public void uiGuessesAgeAndCelebratesIfCorrect() {
+        FakeIO io = new FakeIO("yes");
+        AgeGuesser guesser = new AgeGuesser();
+
+        AgeGuesserUI ui = new AgeGuesserUI(io, guesser);
+        ui.start();
+
+        assertEquals(3, io.output.size());
+
+        String expectedFirstLine = "I will guess your age";
+        String expectedSecondLine = String.format("Are you %d years old? ", guesser.guess());
+        String expectedThirdLine = "Hooray! I only needed 0 hints";
+
+        assertTrue("first message wasn't instructions",
+                io.output.get(0).contains(expectedFirstLine));
+
+        assertTrue("second message doesn't contain the guess",
+                io.output.get(1).contains(expectedSecondLine));
+
+        assertTrue("third message doesn't contain a count of guesses",
+                io.output.get(2).contains(expectedThirdLine));
+    }
+
+    @Test
+    public void uiKeepsGuessingAgeUntilCorrect() {
+        FakeIO io = new FakeIO("higher", "lower", "yes");
+
+        AgeGuesserUI ui = new AgeGuesserUI(io, new AgeGuesser());
+        ui.start();
+
+        assertEquals(5, io.output.size());
+
+        String ageQuestionRegex = "Are you \\d+ years old.*";
+
+        assertTrue(io.output.get(1).matches(ageQuestionRegex));
+        assertTrue(io.output.get(2).matches(ageQuestionRegex));
+        assertTrue(io.output.get(3).matches(ageQuestionRegex));
+    }
+
+    @Test
+    public void uiTellsUserWhenItGetsAnInvalidCommandAndContinues() {
+        FakeIO io = new FakeIO("aljsfl;kasjdf", "yes");
+
+        AgeGuesserUI ui = new AgeGuesserUI(io, new AgeGuesser());
+        ui.start();
+
+        assertEquals(5, io.output.size());
+
+        String secondLine = io.output.get(2);
+        String expectedSecondLine = "I didn't understand \"aljsfl;kasjdf\"";
+        String lastLine = io.output.get(4);
+
+        assertTrue("Expected invalid command message but got " + secondLine, secondLine.contains(expectedSecondLine));
+        assertTrue("Expected Hooray but got " + lastLine, lastLine.contains("Hooray!"));
+    }
+
+}

src/test/java/com/dacklabs/ageguesser/FakeIO.java

@@ -0,0 +1,30 @@
+package com.dacklabs.ageguesser;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class FakeIO implements ConsoleIO {
+
+    private int lineIndex = 0;
+    private final String[] lines;
+
+    // This is public so the test can inspect it easily
+    public final List<String> output = new ArrayList<>();
+
+    // lines are what will pretend to be coming from System.in
+    public FakeIO(String... lines) {
+        this.lines = lines;
+    }
+
+    @Override
+    public String getUserInput() {
+        // return the next line that was passed in
+        return lines[lineIndex++];
+    }
+
+    @Override
+    public void printLine(String line) {
+        // the SUT calls this, and we just record it for later inspection
+        output.add(line);
+    }
+}