diff --git a/t/04-plot_fit.t b/t/04-plot_fit.t
new file mode 100644
index 0000000..b8e7758
--- /dev/null
+++ b/t/04-plot_fit.t
@@ -0,0 +1,66 @@
+use strict;
+use warnings;
+
+use Test::More;
+
+use File::Temp qw(tempfile);
+use FindBin;
+use PDL;
+use PDL::NiceSlice;
+use Physics::Ellipsometry::VASE;
+
+my $vase = Physics::Ellipsometry::VASE->new(layers => 1);
+$vase->load_data("$FindBin::Bin/data/sample.dat");
+
+my $model = sub {
+    my ($params, $x) = @_;
+
+    my $a = $params->(0);
+    my $b = $params->(1);
+    my $c = $params->(2);
+    my $d = $params->(3);
+
+    my $wavelength = $x->(:,0);
+
+    my $psi   = $a - $b * $wavelength;
+    my $delta = $c + $d * $wavelength;
+
+    return cat($psi, $delta)->flat;
+};
+
+ok $vase->set_model($model), 'set_model works';
+
+my $initial_params = pdl [65, 0.05, 80, 0.1];
+my $fit_params = $vase->fit($initial_params);
+
+is_deeply [list $fit_params], [65.0, 0.05, 80.0, 0.10], 'fit parameters correct';
+
+subtest 'find MSE' => sub {
+    my $mse = $vase->mse($fit_params, nparams => 4);
+    ok $mse < 0.000001, 'Mean Squared Error very small';
+    is $mse, 0, 'Mean Squared Error is zero';
+    ok $vase->{iters} > 0, 'Iterations positive';
+};
+
+my ($fh1, $test_plot_png) = tempfile(SUFFIX => '.png', UNLINK => 1);
+my ($fh2, $test_plot_pdf) = tempfile(SUFFIX => '.pdf', UNLINK => 1);
+
+subtest 'Save plot to PNG' => sub {
+    ok $vase->plot($fit_params, output => $test_plot_png),
+        'can plot a png image';
+    ok -e $test_plot_png, "test image $test_plot_png exists";
+    ok -s $test_plot_png, "test image $test_plot_png not empty";
+};
+close $fh1;
+
+subtest 'Save plot to PDF' => sub {
+    ok $vase->plot($fit_params,
+            output => $test_plot_pdf,
+            title => 'Linear Model Fit'),
+        'can plot a pdf file';
+    ok -e $test_plot_pdf, "test image $test_plot_pdf exists";
+    ok -s $test_plot_pdf, "test image $test_plot_pdf not empty";
+};
+close $fh2;
+
+done_testing();