diff --git a/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/service/StockFileParser.java b/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/service/StockFileParser.java
index b08558d..07fd802 100644
--- a/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/service/StockFileParser.java
+++ b/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/service/StockFileParser.java
@@ -3,7 +3,9 @@
 import edu.ntnu.idi.idatt2003.g40.mappe.model.Stock;
 import java.math.BigDecimal;
 import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
 
 /**
  * Converts stock objects to/from string format for file handling.
@@ -42,29 +44,29 @@ public List<Stock> getStocksFromStrings(final List<String> validStocks)
                                           throws IllegalArgumentException {
     if (validStocks == null || validStocks.isEmpty()) {
       throw new IllegalArgumentException("Empty or null stock list!");
-    } else {
-      List<Stock> stocksFromFile = new ArrayList<>();
-      List<String> stockSymbols = new ArrayList<>();
+    }
+    List<Stock> stocksFromFile = new ArrayList<>();
+    Set<String> stockSymbols = new HashSet<>();
 
-      validStocks.forEach(s -> {
-        String[] lineElements = s.split(",");
-        String stockSymbol = lineElements[0].trim();
-        String stockName = lineElements[1].trim();
-        BigDecimal stockPrice = new BigDecimal(lineElements[2].trim());
+    validStocks.forEach(s -> {
+      String[] lineElements = s.split(",");
+      String stockSymbol = lineElements[0].trim();
+      String stockName = lineElements[1].trim();
+      BigDecimal stockPrice = new BigDecimal(lineElements[2].trim());
 
-        try {
-          Stock stockObject = new Stock(stockSymbol, stockName, stockPrice);
-          if (!stockSymbols.contains(stockSymbol)) {
-            stockSymbols.add(stockSymbol);
-            stocksFromFile.add(stockObject);
-          }
-        } catch (IllegalArgumentException e) {
-          System.err.println("(" + s + ") is not a valid stock! Skipping...");
+      try {
+        Stock stockObject = new Stock(stockSymbol, stockName, stockPrice);
+        if (stockSymbols.add(stockSymbol)) {
+          stocksFromFile.add(stockObject);
         }
-
-      });
-      return stocksFromFile;
+      } catch (IllegalArgumentException _) {
+          // Ignore invalid strings.
+      }
+    });
+    if (stocksFromFile.isEmpty()) {
+      throw new IllegalArgumentException("No stocks parsed succesfully!");
     }
+    return stocksFromFile;
   }
 
   /**
@@ -81,13 +83,21 @@ public List<Stock> getStocksFromStrings(final List<String> validStocks)
   public List<String> stocksToStrings(final List<Stock> stocks) {
     if (stocks == null || stocks.isEmpty()) {
       throw new IllegalArgumentException("Empty or null stock list!");
-    } else {
-      ArrayList<String> stringList = new ArrayList<>();
-      stocks.forEach(s ->
-              stringList.add(s.getSymbol().trim() + "," + s.getCompany().trim()
-                      + "," + s.getSalesPrice().toString())
+    }
+
+    List<String> stringList = new ArrayList<>();
+    for (Stock s : stocks) {
+      if (s == null) {
+        continue;
+      }
+
+      String csvRow = String.format("%s, %s, %s",
+              s.getSymbol().trim(),
+              s.getCompany().trim(),
+              s.getSalesPrice().toPlainString()
       );
-      return stringList;
+      stringList.add(csvRow);
     }
+    return stringList;
   }
 }
diff --git a/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/service/StockFileManagerTest.java b/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/service/StockFileManagerTest.java
index 81d5f95..74f0470 100644
--- a/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/service/StockFileManagerTest.java
+++ b/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/service/StockFileManagerTest.java
@@ -1,9 +1,7 @@
 package edu.ntnu.idi.idatt2003.g40.mappe.service;
 
-import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
-import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.io.IOException;
diff --git a/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/service/StockFileParserTest.java b/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/service/StockFileParserTest.java
index 61ecfb2..8fe5158 100644
--- a/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/service/StockFileParserTest.java
+++ b/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/service/StockFileParserTest.java
@@ -1,30 +1,37 @@
 package edu.ntnu.idi.idatt2003.g40.mappe.service;
 
 import edu.ntnu.idi.idatt2003.g40.mappe.model.Stock;
+
+import java.math.BigDecimal;
+import java.util.ArrayList;
+import java.util.List;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
-import java.util.ArrayList;
-import java.util.List;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 
 class StockFileParserTest {
 
-  private StockFileParser converter;
+  /**
+   * Test stock parser to use.
+   * */
+  private StockFileParser testParser;
 
-  private String validStockAsString1;
-  private String validStockAsString2;
-  private String validStockAsString3;
+  /**
+   * List of strings containing valid and invalid representations
+   * of stocks.
+   * */
   private ArrayList<String> allStocks;
-  private String invalidStockAsString1;
 
   @BeforeEach
   void setUp() {
-    validStockAsString1 = "AAPL, Apple inc., 251.42";
-    validStockAsString2 = "NVID, Nvidia corp., 100.25";
-    validStockAsString3 = "SAMS, Samsung corporation, 103.21";
+    String validStockAsString1 = "AAPL, Apple inc., 251.42";
+    String validStockAsString2 = "NVID, Nvidia corp., 100.25";
+    String validStockAsString3 = "SAMS, Samsung corporation, 103.21";
 
-    invalidStockAsString1 = "INVALID, This stock has an invalid code!, 100.21";
+    String invalidStockAsString1 = "INVALID, This stock has an invalid code!, 100.21";
 
     allStocks = new ArrayList<>();
 
@@ -33,15 +40,15 @@ void setUp() {
     allStocks.add(validStockAsString3);
     allStocks.add(invalidStockAsString1);
 
-    converter = new StockFileParser();
+    testParser = new StockFileParser();
   }
 
   @Test
-  void converter_returns_valid_stock_apple() {
+  void getStocksFromStringsReturnsValidStocks() {
 
     boolean stockIncluded = false;
 
-    List<Stock> stocksFromConverter = converter.getStocksFromStrings(allStocks);
+    List<Stock> stocksFromConverter = testParser.getStocksFromStrings(allStocks);
 
     for (Stock s : stocksFromConverter) {
       if (s.getSymbol().equals("AAPL")) {
@@ -54,11 +61,11 @@ void converter_returns_valid_stock_apple() {
   }
 
   @Test
-  void converter_ignores_invalid_stock_representation() {
+  void getStocksFromStringsIgnoresInvalidStocks() {
 
     boolean stockIncluded = false;
 
-    List<Stock> stocksFromConverter = converter.getStocksFromStrings(allStocks);
+    List<Stock> stocksFromConverter = testParser.getStocksFromStrings(allStocks);
 
     for (Stock s : stocksFromConverter) {
       if (s.getSymbol().equals("INVALID")) {
@@ -69,4 +76,30 @@ void converter_ignores_invalid_stock_representation() {
 
     Assertions.assertFalse(stockIncluded);
   }
+
+  @Test
+  void stocksToStringsConvertsValidStocksToCsvFormat() {
+    Stock apple = new Stock("AAPL", "Apple Inc", new BigDecimal("175.50"));
+    Stock tesla = new Stock("TSLA", "Tesla Inc", new BigDecimal("200.00"));
+    List<Stock> stocks = List.of(apple, tesla);
+
+    List<String> result = testParser.stocksToStrings(stocks);
+
+    assertEquals(2, result.size());
+    assertEquals("AAPL, Apple Inc, 175.50", result.get(0));
+    assertEquals("TSLA, Tesla Inc, 200.00", result.get(1));
+  }
+
+  @Test
+  void stocksToStringsThrowsExceptionOnNullOrEmptyList() {
+    List<Stock> emptyList = new ArrayList<>();
+
+    assertThrows(IllegalArgumentException.class,
+            () -> testParser.stocksToStrings(null)
+    );
+
+    assertThrows(IllegalArgumentException.class,
+            () -> testParser.stocksToStrings(emptyList)
+    );
+  }
 }
\ No newline at end of file