In-memory database testing in JUnit - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an in-memory H2 database connection.

JUnit

Connection conn = DriverManager.getConnection("jdbc:h2:[1]", "sa", "");

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Azip:testdb

Bfile:testdb

Ctcp://localhost/testdb

Dmem:testdb

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'file:' instead of 'mem:' causes the database to be file-based, not in-memory.

Forgetting the 'mem:' prefix leads to connection errors.

The correct JDBC URL for an in-memory H2 database starts with 'jdbc:h2:mem:'.

2fill in blank

medium

Complete the code to create a JUnit 5 test method that initializes the in-memory database.

JUnit

@Test
void testDatabaseConnection() throws SQLException {
    Connection conn = DriverManager.getConnection("jdbc:h2:mem:testdb", "sa", "");
    Statement stmt = conn.createStatement();
    stmt.execute([1]);
    conn.close();
}

Drag options to blanks, or click blank then click option'

A"SELECT * FROM users"

B"DROP TABLE users"

C"CREATE TABLE users(id INT PRIMARY KEY, name VARCHAR(255))"

D"INSERT INTO users VALUES(1, 'Alice')"

Attempts:

3 left

💡 Hint

Common Mistakes

Using SELECT or DROP statements before creating the table causes errors.

Trying to insert data before creating the table leads to failures.

To initialize the database, you create the table first using a CREATE TABLE statement.

3fill in blank

hard

Fix the error in the assertion that checks if the user count is 1.

JUnit

ResultSet rs = stmt.executeQuery("SELECT COUNT(*) FROM users");
rs.next();
assertEquals([1], rs.getInt(1));

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A0

B1

C"1"

Drs.getString(1)

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string '1' instead of integer 1 causes assertion failure.

Using 0 as expected count is incorrect if one row was inserted.

The count should be compared as an integer 1, not as a string or zero.

4fill in blank

hard

Fill both blanks to insert a user and verify the insertion.

JUnit

stmt.executeUpdate("INSERT INTO users (id, name) VALUES ([1], '[2]')");
ResultSet rs = stmt.executeQuery("SELECT name FROM users WHERE id = 1");
rs.next();
assertEquals("Alice", rs.getString(1));

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A1

BAlice

C2

DBob

Attempts:

3 left

💡 Hint

Common Mistakes

Using id 2 or name 'Bob' causes the assertion to fail.

Mismatching inserted values and assertion expected values.

The inserted user has id 1 and name 'Alice' to match the assertion.

5fill in blank

hard

Fill all three blanks to create a test that inserts multiple users and checks their count.

JUnit

stmt.executeUpdate("INSERT INTO users (id, name) VALUES ([1], '[2]')");
stmt.executeUpdate("INSERT INTO users (id, name) VALUES ([3], 'Bob')");
ResultSet rs = stmt.executeQuery("SELECT COUNT(*) FROM users");
rs.next();
assertEquals([4], rs.getInt(1));

Drag options to blanks, or click blank then click option'

A1

BAlice

C2

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same id for both inserts causes primary key errors.

Expecting count 1 after inserting two users causes assertion failure.

Insert user with id 1 named Alice, user with id 2 named Bob, and expect count 2.