Junit for generateToken() method for JWT in Springboot - spring-boot

Question

public String generateToken(final String id) {
Claims claims = Jwts.claims().setSubject(id);
long nowMillis = System.currentTimeMillis();
long expMillis = nowMillis + tokenValidity;
Date exp = new Date(expMillis);
return Jwts.builder().setClaims(claims).setIssuedAt(new Date(nowMillis)).setExpiration(exp)
.signWith(SignatureAlgorithm.HS512, jwtSecret).compact();
}
Now I want to write JUnit for this method and I am trying like below, but I am getting error
#Test
#Order(1)
public void test_generateToken() throws JwtTokenMalformedException, JwtTokenMissingException {
final String subject_id = "123456789";
final Long tokenValidity = 180000L;
final String jwtSecret = "jwtSecret";
when(Jwts.claims().setSubject(subject_id)).thenReturn(new DefaultClaims()); //** line no: 10
when(Jwts.builder().setClaims(claims).setIssuedAt(new Date(nowMillis)).setExpiration(exp)
.signWith(SignatureAlgorithm.HS512, jwtSecret).compact()).thenReturn(new String());
}
getting error at line number 10:
org.mockito.exceptions.misusing.MissingMethodInvocationException:
when() requires an argument which has to be 'a method call on a mock'.
For example:
when(mock.getArticles()).thenReturn(articles);
Also, this error might show up because:
1. you stub either of: final/private/equals()/hashCode() methods.
Those methods *cannot* be stubbed/verified.
Mocking methods declared on non-public parent classes is not supported.
2. inside when() you don't call method on mock but on some other > object.

Answer 1

Two problems need to be solved in your code: mocking static methods and multiple chained calls on a mocked object. Please, find the code with inline comments below as well as some references for further reading. Important note: mockito-inline should be used (see docs links below).
void test_generateToken() {
var tested = new TestedClass();
var jwtSecret = "jwtSecret";
var claims = new DefaultClaims();
var mockedValue = "mocked value";
var builder = mock(Jwts.JwtsBuilder.class, RETURNS_DEEP_STUBS);
try (var mockedStatic = mockStatic(Jwts.class)) {
// to mock static methods the object returned from the mockStatic method should be used
mockedStatic.when(Jwts::claims)
.thenReturn(claims);
mockedStatic.when(Jwts::builder)
.thenReturn(builder);
// here we're not mocking static methods, so a standard when method is used
// thanks to RETURNS_DEEP_STUBS we can mock a chain of method calls
when(builder.setClaims(claims)
// other argument matchers like argThat() can be used here
.setIssuedAt(any())
.setExpiration(any())
.signWith(SignatureAlgorithm.HS512, jwtSecret)
.compact())
.thenReturn(mockedValue);
var result = tested.generateToken("value");
assertEquals(mockedValue, result);
}
}
mockStatic method docs
example of static mocking from the docs
RETURNS_DEEP_STUBS docs
ArgumentMatchers docs (see: any(), argThat())
mockito-inline docs
I've created a commit in a GitHub repository, where you can find the code above as well as mockito-inline dependency reference and a few fake classes representing the missing code from your question (which is not important as it's all mocked). The test shown in the example passes.