diff --git a/.gitignore b/.gitignore
index acec74a..c132588 100644
--- a/.gitignore
+++ b/.gitignore
@@ -58,3 +58,4 @@ local.properties
 # Uncomment this line if you wish to ignore the project description file.
 # Typically, this file would be tracked if it contains build/dependency configurations:
 #.project
+.DS_Store
diff --git a/src/edu/mills/cs180a/StringUtilitiesTester.java b/src/edu/mills/cs180a/StringUtilitiesTester.java
index dfeabf9..c52dfe3 100644
--- a/src/edu/mills/cs180a/StringUtilitiesTester.java
+++ b/src/edu/mills/cs180a/StringUtilitiesTester.java
@@ -1,10 +1,15 @@
 package edu.mills.cs180a;
 
+import static org.junit.Assert.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 
 class StringUtilitiesTester {
+    
+
     @Test
     void isSubstringThrowsExceptionForNullArg() {
         assertThrows(NullPointerException.class, () -> StringUtilities.isSubstring(null, "foo"));
@@ -17,9 +22,27 @@ void isSubstringReturnsTrueForEmptySubstring() {
         assertTrue(StringUtilities.isSubstring("", "foo"));
     }
 
-    @Test
-    void isSubstringReturnsTrueForLengthOneSubstring() {
-        assertTrue(StringUtilities.isSubstring("A", "ABC"));
-        // TODO: write rest
+    @ParameterizedTest
+    @CsvSource(value = {"A:ABC","B:ABC","C:ABC"}, delimiter = ':')
+    void isSubstringReturnsTrueForLengthOneSubstring(String substring, String text) {
+        assertTrue(StringUtilities.isSubstring(substring, text));
+    }
+    
+    @ParameterizedTest
+    @CsvSource(value = {"D:ABC","B:ABC","A:ABC", "E:ABC"}, delimiter = ':')
+    void isSubstringReturnsFalseForLengthOneSubstring(String substring, String text) {
+        assertFalse(StringUtilities.isSubstring(substring, text));
+    }
+    
+    @ParameterizedTest
+    @CsvSource(value = {"AB:ABC","BC:ABC","CD:ABCD"}, delimiter = ':')
+    void isSubstringReturnsTrueForLengthTwoSubstring(String substring, String text) {
+        assertTrue(StringUtilities.isSubstring(substring, text));
+    }
+    
+    @ParameterizedTest
+    @CsvSource(value = {"DE:ABC", "EF:ABCDE"}, delimiter = ':')
+    void isSubstringReturnsFalseForLengthTwoSubstring(String substring, String text) {
+        assertFalse(StringUtilities.isSubstring(substring, text));
     }
 }