You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: test_circuit.rs
    path of file: ./repos/snarkVM/algorithms/src/snark/varuna/data_structures
    
    the code of the file until where you have to start completion: // Copyright (C) 2019-2023 Aleo Systems Inc.
// This file is part of the snarkVM library.

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at:
// http://www.apache.org/licenses/LICENSE-2.0

// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use crate::r1cs::{ConstraintSynthesizer, ConstraintSystem, SynthesisError};
use snarkvm_fields::Field;

use rand::{CryptoRng, Rng};

#[doc(hidden)]
#[derive(Clone)]
/// This Circuit is only for testing and should not be used in production
pub struct TestCircuit<F: Field> {
    pub a: Option<F>,
    pub b: Option<F>,
    pub num_constraints: usize,
    pub num_variables: usize,
    pub mul_depth: usize,
}

impl<F: Field> core::fmt::Debug for TestCircuit<F> {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        write!(
            f,
            "TestCircuit {{ num_constraints: {}, num_variables: {}, mul_depth: {} }}",
            self.num_constraints, self.num_variables, self.mul_depth
        )
    }
}

impl<ConstraintF: Field> ConstraintSynthesizer<ConstraintF> for TestCircuit<ConstraintF> {
    fn generate_constraints<CS: ConstraintSystem<ConstraintF>>(&self, cs: &mut CS) -> Result<(), SynthesisError> {
        // Ensure the given `cs` is starting off clean.
        assert_eq!(1, cs.num_public_variables());
        assert_eq!(0, cs.num_private_variable
    
    fn generate_constraints<CS: ConstraintSystem<ConstraintF>>(&self, cs: &mut CS) -> Result<(), SynthesisError> {
        // Ensure the given `cs` is starting off clean.
        assert_eq!(1, cs.num_public_variables());
        assert_eq!(0, cs.num_private_variables());
        assert_eq!(0, cs.num_constraints());

        let a = cs.alloc(|| "a", || self.a.ok_or(SynthesisError::AssignmentMissing))?;
        let b = cs.alloc(|| "b", || self.b.ok_or(SynthesisError::AssignmentMissing))?;

        let mut mul_vars = Vec::with_capacity(self.mul_depth);
        for i in 0..self.mul_depth {
            let mul_var = cs.alloc_input(
                || format!("mul_var {i}"),
                || {
                    let mut a = self.a.ok_or(SynthesisError::AssignmentMissing)?;
                    let b = self.b.ok_or(SynthesisError::AssignmentMissing)?;

                    for _ in 0..(1 + i) {
                        a.mul_assign(&b);
                    }
                    Ok(a)
                },
            )?;
            mul_vars.push(mul_var);
        }

        // For this test we should allocate self.num_variables number of variables
        // 2 + mul_depth variables were already allocated above, 1 is allocated by default
        let dummy_variables = self.num_variables - 3 - self.mul_depth;
        for i in 0..dummy_variables {
            let _ = cs.alloc(|| format!("var {i}"), || self.a.ok_or(SynthesisError::AssignmentMissing))?;
        }

        let mul_constraints = self.mul_depth - 1;
        for i in 0..(self.num_constraints - mul_constraints) {
            cs.enforce(|| format!("constraint {i}"), |lc| lc + a, |lc| lc + b, |lc| lc + mul_vars[0]);
        }

        for i in 0..mul_constraints {
            cs.enforce(|| format!("constraint_mul {i}"), |lc| lc + mul_vars[i], |lc| lc + b, |lc| lc + mul_vars[i + 1]);
        }

        assert_eq!(cs.num_constraints(), self.num_constraints);
        assert_eq!(cs.num_public_variables() + cs.num_private_variables(), self.num_variables);

        Ok(())
    }