Create InMemoryFileSystem for testing purposes

build.gradle

@@ -12,10 +12,8 @@ buildscript {
         maven {
             url = 'https://oss.sonatype.org/service/local/staging/deploy/maven2/'
         }
-
-        jcenter()
-
         google()
+        jcenter()
     }
 
     rootProject.ext.versions = [

filesystem/src/main/java/com/nytimes/android/external/fs3/filesystem/InMemoryFileSystem.java

@@ -0,0 +1,73 @@
+package com.nytimes.android.external.fs3.filesystem;
+
+import com.nytimes.android.external.store3.base.RecordState;
+import okio.BufferedSource;
+
+import javax.annotation.Nonnull;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.concurrent.TimeUnit;
+
+
+/**
+ * This {@link FileSystem} has been created for testing purposes only, especially on Android, when you might need
+ * to avoid storing all the information.
+ *
+ * It is not suitable for production.
+ */
+@Deprecated
+public class InMemoryFileSystem implements FileSystem {
+
+    private Map<String, BufferedSource> fs = new HashMap<>();
+
+    @Nonnull
+    @Override
+    public BufferedSource read(String path) throws FileNotFoundException {
+        if (fs.containsKey(path)) {
+            return fs.get(path);
+        } else {
+            throw new FileNotFoundException("File " + path + " was not found in memory");
+        }
+    }
+
+    @Override
+    public void write(String path, BufferedSource source) throws IOException {
+        fs.put(path, source);
+    }
+
+    @Override
+    public void delete(String path) throws IOException {
+        fs.remove(path);
+    }
+
+    @Override
+    public void deleteAll(String path) throws IOException {
+        fs.clear();
+    }
+
+    @Nonnull
+    @Override
+    public Collection<String> list(String path) throws FileNotFoundException {
+        if (fs.isEmpty()) {
+            throw new FileNotFoundException("Memory is empty");
+        }
+        return fs.keySet();
+    }
+
+    @Override
+    public boolean exists(String file) {
+        return fs.containsKey(file);
+    }
+
+    @Override
+    public RecordState getRecordState(@Nonnull TimeUnit expirationUnit, long expirationDuration, @Nonnull String path) {
+        if (fs.containsKey(path)) {
+            return RecordState.FRESH;
+        } else {
+            return RecordState.MISSING;
+        }
+    }
+}