Add test for magnetic pickup

tests/diagnostics/test_magnetic_pickup_probe.py

@@ -0,0 +1,35 @@
+"""Unit test for the magnetic pickup probe (B-dot probe) diagnostics."""
+
+import numpy as np
+import astropy.units as u
+import pytest
+
+from plasmapy.diagnostics.magnetic_pickup_probe import compute_bfield
+
+
+def test_compute_bfield_integrates_voltage_to_field():
+    """
+    Test compute_bfield by inputting a sine wave voltage and checking
+    if the output magnetic field matches the integrated waveform.
+    """
+    # Create a time array in seconds
+    time = np.linspace(0, 2 * np.pi, 1000) * u.s
+
+    # Create a sine voltage signal: V(t) = sin(t)
+    voltage = np.sin(time.value) * u.V
+
+    # Set probe parameters
+    loop_area = 1.0 * u.m**2
+    num_loop = 1
+    gain = 1.0
+
+    # Expected magnetic field is the integral of V(t)/(N*A*gain)
+    expected_field = -np.cos(time.value) + 1  # Integral of sin(t) is -cos(t), plus constant
+    expected_field *= (1 / (loop_area * num_loop * gain)).value  # Apply scaling
+    expected_field = expected_field * u.T  # Assign Tesla units
+
+    # Compute B field using function
+    computed_bfield = compute_bfield(voltage, time, loop_area, num_loop, gain)
+
+    # Use a tolerance since numerical integration introduces small errors
+    assert u.allclose(computed_bfield, expected_field, rtol=1e-3, atol=1e-5 * u.T)