diff --git a/.travis.yml b/.travis.yml
index 705ea2eb..c0eb7f08 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -10,3 +10,8 @@ before_install:
 
 script:
   - docker run java/koans /bin/bash -c "git clone https://github.com/matyb/java-koans && gradle -p java-koans/lib buildApp"
+
+cache:
+  directories:
+  - $HOME/.gradle/caches/
+  - $HOME/.gradle/wrapper/
diff --git a/koans/src/beginner/AboutPrimitives.java b/koans/src/beginner/AboutPrimitives.java
index f8a240b5..2f196653 100644
--- a/koans/src/beginner/AboutPrimitives.java
+++ b/koans/src/beginner/AboutPrimitives.java
@@ -117,7 +117,7 @@ public void primitivesOfTypeCharHaveAnObjectTypeCharacter() {
     }
 
     @Koan
-    public void charsCanOnlyBePositive() {
+    public void charsAreNotNegative() {
         assertEquals((int) Character.MIN_VALUE, __);
         assertEquals((int) Character.MAX_VALUE, __);
 
diff --git a/koans/src/intermediate/AboutFileIO.java b/koans/src/intermediate/AboutFileIO.java
index 4649ebc9..3fb98e7d 100644
--- a/koans/src/intermediate/AboutFileIO.java
+++ b/koans/src/intermediate/AboutFileIO.java
@@ -12,7 +12,7 @@ public class AboutFileIO {
 
     @Koan
     public void fileObjectDoesntCreateFile() {
-        File f = new File("foo.txt");
+        File f = new File("i-never.exist");
         assertEquals(f.exists(), __);
     }
 
@@ -29,11 +29,12 @@ public void fileCreationAndDeletion() throws IOException {
     public void basicFileWritingAndReading() throws IOException {
         File file = new File("file.txt");
         FileWriter fw = new FileWriter(file);
-        fw.write("First line\nSecond line");
+        String data = "First line\nSecond line";
+        fw.write(data);
         fw.flush();
         fw.close();
 
-        char[] in = new char[50];
+        char[] in = new char[data.length()];
         int size = 0;
         FileReader fr = new FileReader(file);
         size = fr.read(in);
diff --git a/koans/src/java8/AboutStreams.java b/koans/src/java8/AboutStreams.java
index 42e7b2db..ee0c90e4 100644
--- a/koans/src/java8/AboutStreams.java
+++ b/koans/src/java8/AboutStreams.java
@@ -68,13 +68,6 @@ public void join() {
         assertEquals(join, __);
     }
 
-    @Koan
-    public void reduceWithBinaryOperator() {
-        String join = places.stream()
-                .reduce("", String::concat);
-        assertEquals(join, __);
-    }
-
     @Koan
     public void stringJoin() {
         String join = places.stream()