diff --git a/tests/functional/doubles_test.sh b/tests/functional/doubles_test.sh
new file mode 100644
index 00000000..1bee6f11
--- /dev/null
+++ b/tests/functional/doubles_test.sh
@@ -0,0 +1,64 @@
+#!/bin/bash
+
+function test_mock_ps_when_executing_a_script() {
+  mock ps cat ./tests/functional/fixtures/doubles_ps_output
+
+  assert_match_snapshot "$(./tests/functional/fixtures/doubles_script.sh)"
+}
+
+function test_mock_ps_when_executing_a_sourced_function() {
+  source ./tests/functional/fixtures/doubles_function.sh
+  mock ps cat ./tests/functional/fixtures/doubles_ps_output
+
+  assert_match_snapshot "$(top_mem)"
+}
+
+function test_spy_commands_called_when_executing_a_script() {
+  spy ps
+  spy awk
+  spy head
+
+  ./tests/functional/fixtures/doubles_script.sh
+
+  assert_have_been_called ps
+  assert_have_been_called awk
+  assert_have_been_called head
+}
+
+function test_spy_commands_called_when_executing_a_sourced_function() {
+  source ./tests/functional/fixtures/doubles_function.sh
+  spy ps
+  spy awk
+  spy head
+
+  top_mem
+
+  assert_have_been_called ps
+  assert_have_been_called awk
+  assert_have_been_called head
+}
+
+function test_spy_commands_called_once_when_executing_a_script() {
+  spy ps
+  spy awk
+  spy head
+
+  ./tests/functional/fixtures/doubles_script.sh
+
+  assert_have_been_called_times 1 ps
+  assert_have_been_called_times 1 awk
+  assert_have_been_called_times 1 head
+}
+
+function test_spy_commands_called_once_when_executing_a_sourced_function() {
+  source ./tests/functional/fixtures/doubles_function.sh
+  spy ps
+  spy awk
+  spy head
+
+  top_mem
+
+  assert_have_been_called_times 1 ps
+  assert_have_been_called_times 1 awk
+  assert_have_been_called_times 1 head
+}
diff --git a/tests/functional/fixtures/doubles_function.sh b/tests/functional/fixtures/doubles_function.sh
old mode 100644
new mode 100755
diff --git a/tests/functional/fixtures/doubles_script.sh b/tests/functional/fixtures/doubles_script.sh
old mode 100644
new mode 100755
diff --git a/tests/functional/snapshots/doubles_test_sh.test_mock_ps_when_executing_a_script.snapshot b/tests/functional/snapshots/doubles_test_sh.test_mock_ps_when_executing_a_script.snapshot
new file mode 100644
index 00000000..77519f53
--- /dev/null
+++ b/tests/functional/snapshots/doubles_test_sh.test_mock_ps_when_executing_a_script.snapshot
@@ -0,0 +1,3 @@
+firefox                      2.0
+Xorg                         1.6
+jetbrains-toolbox            1.3
diff --git a/tests/functional/snapshots/doubles_test_sh.test_mock_ps_when_executing_a_sourced_function.snapshot b/tests/functional/snapshots/doubles_test_sh.test_mock_ps_when_executing_a_sourced_function.snapshot
new file mode 100644
index 00000000..77519f53
--- /dev/null
+++ b/tests/functional/snapshots/doubles_test_sh.test_mock_ps_when_executing_a_sourced_function.snapshot
@@ -0,0 +1,3 @@
+firefox                      2.0
+Xorg                         1.6
+jetbrains-toolbox            1.3