ec2_ami: unit-test coverage

Partial unit-test coverage of the `ec2_ami`.

changelogs/fragments/ec2_ami_test-coverage.yaml

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+---
+minor_changes:
+- "ec2_ami - Extend the unit-test coverage of the module (https://github.com/ansible-collections/amazon.aws/pull/1159)."

tests/unit/plugins/modules/test_ec2_ami.py

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+#!/usr/bin/env python3
+
+from unittest.mock import MagicMock, Mock, patch, call
+
+import pytest
+
+from ansible_collections.amazon.aws.plugins.modules import ec2_ami
+
+module_name = "ansible_collections.amazon.aws.plugins.modules.ec2_ami"
+
+
+def test_get_block_device_mapping_virtual_name():
+    image = {
+        "block_device_mappings": [
+            {"device_name": "/dev/sdc", "virtual_name": "ephemeral0"}
+        ]
+    }
+    block_device = ec2_ami.get_block_device_mapping(image)
+    assert block_device == {"/dev/sdc": {"virtual_name": "ephemeral0"}}
+
+
+def test_get_image_by_id_found():
+    module = MagicMock()
+    connection = MagicMock()
+
+    connection.describe_images.return_value = {
+        "Images": [{"ImageId": "ami-0c7a795306730b288"}]
+    }
+
+    image = ec2_ami.get_image_by_id(module, connection, "ami-0c7a795306730b288")
+    assert image["ImageId"] == "ami-0c7a795306730b288"
+    assert connection.describe_images.call_count == 1
+    assert connection.describe_image_attribute.call_count == 2
+    connection.describe_images.assert_has_calls(
+        [
+            call(
+                aws_retry=True,
+                ImageIds=["ami-0c7a795306730b288"],
+            )
+        ]
+    )
+
+
+def test_get_image_by_missing():
+    module = MagicMock()
+    connection = MagicMock()
+
+    connection.describe_images.return_value = {"Images": []}
+
+    image = ec2_ami.get_image_by_id(module, connection, "ami-0c7a795306730b288")
+    assert image is None
+    assert connection.describe_images.call_count == 1
+    connection.describe_images.assert_has_calls(
+        [
+            call(
+                aws_retry=True,
+                ImageIds=["ami-0c7a795306730b288"],
+            )
+        ]
+    )
+
+
+@patch(
+    module_name + ".get_image_by_id",
+)
+def test_create_image_minimal(m_get_image_by_id):
+    module = MagicMock()
+    connection = MagicMock()
+
+    m_get_image_by_id.return_value = {"ImageId": "ami-0c7a795306730b288"}
+    module.params = {
+        "name": "my-image",
+        "instance_id": "i-123456789",
+        "image_id": "ami-0c7a795306730b288",
+    }
+    ec2_ami.create_image(module, connection)
+    assert connection.create_image.call_count == 1
+    connection.create_image.assert_has_calls(
+        [
+            call(
+                aws_retry=True,
+                Description=None,
+                InstanceId="i-123456789",
+                Name="my-image",
+                NoReboot=None,
+            )
+        ]
+    )