Refactor CSV quoting and escaping of strings

Add tests

collect_app/src/main/java/org/odk/collect/android/utilities/CSVUtils.java

@@ -1,5 +1,7 @@
 package org.odk.collect.android.utilities;
 
+import org.jetbrains.annotations.Contract;
+
 public class CSVUtils {
 
     private CSVUtils() {
@@ -9,11 +11,32 @@ private CSVUtils() {
     /**
      * Escapes quotes and then wraps in quotes for output to CSV.
      */
+    @Contract("null -> null")
     public static String getEscapedValueForCsv(String value) {
+        if (value == null) {
+            return null;
+        }
+
         if (value.contains("\"")) {
-            value = value.replaceAll("\"", "\"\"");
+            value = escapeDoubleQuote(value);
         }
 
+        return quoteString(value);
+    }
+
+    @Contract("null -> null; !null -> !null")
+    public static String escapeDoubleQuote(String value) {
+        if (value == null) {
+            return null;
+        }
+        return value.replaceAll("\"", "\"\"");
+    }
+
+    @Contract(value = "null -> null; !null -> !null", pure = true)
+    public static String quoteString(String value) {
+        if (value == null) {
+            return null;
+        }
         return "\"" + value + "\"";
     }
 }

collect_app/src/test/java/org/odk/collect/android/utilities/CSVUtilsTest.java

@@ -0,0 +1,30 @@
+package org.odk.collect.android.utilities;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class CSVUtilsTest {
+    @Test
+    public void testEscapeDoubleQuote() {
+        Assert.assertNull(CSVUtils.escapeDoubleQuote(null));
+        Assert.assertEquals("", CSVUtils.escapeDoubleQuote(""));
+        Assert.assertEquals("no quotes", CSVUtils.escapeDoubleQuote("no quotes"));
+        Assert.assertEquals("string with \"\"quotes\"\"", CSVUtils.escapeDoubleQuote("string with \"quotes\""));
+    }
+
+    @Test
+    public void testQuoteString() {
+        Assert.assertNull(CSVUtils.quoteString(null));
+        Assert.assertEquals("\"\"", CSVUtils.quoteString(""));
+        Assert.assertEquals("\"string\"", CSVUtils.quoteString("string"));
+        Assert.assertEquals("\"string with \"quotes\"\"", CSVUtils.quoteString("string with \"quotes\""));
+    }
+
+    @Test
+    public void testGetEscapedValueForCsv() {
+        Assert.assertNull(CSVUtils.getEscapedValueForCsv(null));
+        Assert.assertEquals("\"\"", CSVUtils.getEscapedValueForCsv(""));
+        Assert.assertEquals("\"string\"", CSVUtils.getEscapedValueForCsv("string"));
+        Assert.assertEquals("\"string with \"\"quotes\"\"\"", CSVUtils.getEscapedValueForCsv("string with \"quotes\""));
+    }
+}